linux/init/calibrate.c

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/* calibrate.c: default delay calibration
*
* Excised from init/main.c
* Copyright (C) 1991, 1992 Linus Torvalds
*/
#include <linux/jiffies.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/smp.h>
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
unsigned long lpj_fine;
unsigned long preset_lpj;
static int __init lpj_setup(char *str)
{
preset_lpj = simple_strtoul(str,NULL,0);
return 1;
}
__setup("lpj=", lpj_setup);
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
#ifdef ARCH_HAS_READ_CURRENT_TIMER
/* This routine uses the read_current_timer() routine and gets the
* loops per jiffy directly, instead of guessing it using delay().
* Also, this code tries to handle non-maskable asynchronous events
* (like SMIs)
*/
#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
#define MAX_DIRECT_CALIBRATION_RETRIES 5
static unsigned long __cpuinit calibrate_delay_direct(void)
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
{
unsigned long pre_start, start, post_start;
unsigned long pre_end, end, post_end;
unsigned long start_jiffies;
unsigned long timer_rate_min, timer_rate_max;
unsigned long good_timer_sum = 0;
unsigned long good_timer_count = 0;
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
int i;
if (read_current_timer(&pre_start) < 0 )
return 0;
/*
* A simple loop like
* while ( jiffies < start_jiffies+1)
* start = read_current_timer();
* will not do. As we don't really know whether jiffy switch
* happened first or timer_value was read first. And some asynchronous
* event can happen between these two events introducing errors in lpj.
*
* So, we do
* 1. pre_start <- When we are sure that jiffy switch hasn't happened
* 2. check jiffy switch
* 3. start <- timer value before or after jiffy switch
* 4. post_start <- When we are sure that jiffy switch has happened
*
* Note, we don't know anything about order of 2 and 3.
* Now, by looking at post_start and pre_start difference, we can
* check whether any asynchronous event happened or not
*/
for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
pre_start = 0;
read_current_timer(&start);
start_jiffies = jiffies;
while (time_before_eq(jiffies, start_jiffies + 1)) {
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
pre_start = start;
read_current_timer(&start);
}
read_current_timer(&post_start);
pre_end = 0;
end = post_start;
while (time_before_eq(jiffies, start_jiffies + 1 +
DELAY_CALIBRATION_TICKS)) {
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
pre_end = end;
read_current_timer(&end);
}
read_current_timer(&post_end);
timer_rate_max = (post_end - pre_start) /
DELAY_CALIBRATION_TICKS;
timer_rate_min = (pre_end - post_start) /
DELAY_CALIBRATION_TICKS;
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
/*
* If the upper limit and lower limit of the timer_rate is
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
* >= 12.5% apart, redo calibration.
*/
if (pre_start != 0 && pre_end != 0 &&
(timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
good_timer_count++;
good_timer_sum += timer_rate_max;
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
}
}
if (good_timer_count)
return (good_timer_sum/good_timer_count);
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
"estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
return 0;
}
#else
static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
#endif
/*
* This is the number of bits of precision for the loops_per_jiffy. Each
* time we refine our estimate after the first takes 1.5/HZ seconds, so try
* to start with a good estimate.
* For the boot cpu we can skip the delay calibration and assign it a value
* calculated based on the timer frequency.
* For the rest of the CPUs we cannot assume that the timer frequency is same as
* the cpu frequency, hence do the calibration for those.
*/
#define LPS_PREC 8
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
static unsigned long __cpuinit calibrate_delay_converge(void)
{
/* First stage - slowly accelerate to find initial bounds */
unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
int trials = 0, band = 0, trial_in_band = 0;
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
lpj = (1<<12);
/* wait for "start of" clock tick */
ticks = jiffies;
while (ticks == jiffies)
; /* nothing */
/* Go .. */
ticks = jiffies;
do {
if (++trial_in_band == (1<<band)) {
++band;
trial_in_band = 0;
}
__delay(lpj * band);
trials += band;
} while (ticks == jiffies);
/*
* We overshot, so retreat to a clear underestimate. Then estimate
* the largest likely undershoot. This defines our chop bounds.
*/
trials -= band;
loopadd_base = lpj * band;
lpj_base = lpj * trials;
recalibrate:
lpj = lpj_base;
loopadd = loopadd_base;
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
/*
* Do a binary approximation to get lpj set to
* equal one clock (up to LPS_PREC bits)
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
*/
chop_limit = lpj >> LPS_PREC;
while (loopadd > chop_limit) {
lpj += loopadd;
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
ticks = jiffies;
while (ticks == jiffies)
; /* nothing */
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
ticks = jiffies;
__delay(lpj);
if (jiffies != ticks) /* longer than 1 tick */
lpj -= loopadd;
loopadd >>= 1;
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
}
/*
* If we incremented every single time possible, presume we've
* massively underestimated initially, and retry with a higher
* start, and larger range. (Only seen on x86_64, due to SMIs)
*/
if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
lpj_base = lpj;
loopadd_base <<= 2;
goto recalibrate;
}
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
return lpj;
}
void __cpuinit calibrate_delay(void)
{
static bool printed;
if (preset_lpj) {
loops_per_jiffy = preset_lpj;
if (!printed)
pr_info("Calibrating delay loop (skipped) "
"preset value.. ");
} else if ((!printed) && lpj_fine) {
loops_per_jiffy = lpj_fine;
pr_info("Calibrating delay loop (skipped), "
"value calculated using timer frequency.. ");
[PATCH] Platform SMIs and their interferance with tsc based delay calibration Issue: Current tsc based delay_calibration can result in significant errors in loops_per_jiffy count when the platform events like SMIs (System Management Interrupts that are non-maskable) are present. This could lead to potential kernel panic(). This issue is becoming more visible with 2.6 kernel (as default HZ is 1000) and on platforms with higher SMI handling latencies. During the boot time, SMIs are mostly used by BIOS (for things like legacy keyboard emulation). Description: The psuedocode for current delay calibration with tsc based delay looks like (0) Estimate a value for loops_per_jiffy (1) While (loops_per_jiffy estimate is accurate enough) (2) wait for jiffy transition (jiffy1) (3) Note down current tsc (tsc1) (4) loop until tsc becomes tsc1 + loops_per_jiffy (5) check whether jiffy changed since jiffy1 or not and refine loops_per_jiffy estimate Consider the following cases Case 1: If SMIs happen between (2) and (3) above, we can end up with a loops_per_jiffy value that is too low. This results in shorted delays and kernel can panic () during boot (Mostly at IOAPIC timer initialization timer_irq_works() as we don't have enough timer interrupts in a specified interval). Case 2: If SMIs happen between (3) and (4) above, then we can end up with a loops_per_jiffy value that is too high. And with current i386 code, too high lpj value (greater than 17M) can result in a overflow in delay.c:__const_udelay() again resulting in shorter delay and panic(). Solution: The patch below makes the calibration routine aware of asynchronous events like SMIs. We increase the delay calibration time and also identify any significant errors (greater than 12.5%) in the calibration and notify it to user. Patch below changes both i386 and x86-64 architectures to use this new and improved calibrate_delay_direct() routine. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Adrian Bunk <bunk@stusta.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-06-23 07:08:13 +00:00
} else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
if (!printed)
pr_info("Calibrating delay using timer "
"specific routine.. ");
} else {
if (!printed)
pr_info("Calibrating delay loop... ");
calibrate: extract fall-back calculation into own helper The motivation for this patch series is that currently our OMAP calibrates itself using the trial-and-error binary chop fallback that some other architectures no longer need to perform. This is a lengthy process, taking 0.2s in an environment where boot time is of great interest. Patch 2/4 has two optimisations. Firstly, it replaces the initial repeated- doubling to find the relevant power of 2 with a tight loop that just does as much as it can in a jiffy. Secondly, it doesn't binary chop over an entire power of 2 range, it choses a much smaller range based on how much it squeezed in, and failed to squeeze in, during the first stage. Both are significant optimisations, and bring our calibration down from 23 jiffies to 5, and, in the process, often arrive at a more accurate lpj value. The 'bands' and 'sub-logarithmic' growth may look over-engineered, but they only cost a small level of inaccuracy in the initial guess (for all architectures) in order to avoid the very large inaccuracies that appeared during testing (on x86_64 architectures, and presumably others with less metronomic operation). Note that due to the existence of the TSC and other timers, the x86_64 will not typically use this fallback routine, but I wanted to code defensively, able to cope with all kinds of processor behaviours and kernel command line options. Patch 3/4 is an additional trap for the nightmare scenario where the initial estimate is very inaccurate, possibly due to things like SMIs. It simply retries with a larger bound. Stephen said: I tried this patch set out on an MSM7630. : : Before: : : Calibrating delay loop... 681.57 BogoMIPS (lpj=3407872) : : After: : : Calibrating delay loop... 680.75 BogoMIPS (lpj=3403776) : : But the really good news is calibration time dropped from ~247ms to ~56ms. : Sadly we won't be able to benefit from this should my udelay patches make : it into ARM because we would be using calibrate_delay_direct() instead (at : least on machines who choose to). Can we somehow reapply the logic behind : this to calibrate_delay_direct()? That would be even better, but this is : definitely a boot time improvement. : : Or maybe we could just replace calibrate_delay_direct() with this fallback : calculation? If __delay() is a thin wrapper around read_current_timer() : it should work just as well (plus patch 3 makes it handle SMIs). I'll try : that out. This patch: ... so that it can be modified more clinically. This is almost entirely cosmetic. The only change to the operation is that the global variable is only set once after the estimation is completed, rather than taking on all the intermediate values. However, there are no readers of that variable, so this change is unimportant. Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Tested-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Greg KH <greg@kroah.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-22 23:34:12 +00:00
loops_per_jiffy = calibrate_delay_converge();
}
if (!printed)
pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
loops_per_jiffy/(500000/HZ),
(loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
printed = true;
}