linux/arch/x86/kernel/tsc_sync.c

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/*
* check TSC synchronization.
*
* Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
*
* We check whether all boot CPUs have their TSC's synchronized,
* print a warning if not and turn off the TSC clock-source.
*
* The warp-check is point-to-point between two CPUs, the CPU
* initiating the bootup is the 'source CPU', the freshly booting
* CPU is the 'target CPU'.
*
* Only two CPUs may participate - they can enter in any order.
* ( The serial nature of the boot logic and the CPU hotplug lock
* protects against more than 2 CPUs entering this code. )
*/
#include <linux/spinlock.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/nmi.h>
#include <asm/tsc.h>
/*
* Entry/exit counters that make sure that both CPUs
* run the measurement code at once:
*/
static __cpuinitdata atomic_t start_count;
static __cpuinitdata atomic_t stop_count;
/*
* We use a raw spinlock in this exceptional case, because
* we want to have the fastest, inlined, non-debug version
* of a critical section, to be able to prove TSC time-warps:
*/
static __cpuinitdata raw_spinlock_t sync_lock = __RAW_SPIN_LOCK_UNLOCKED;
static __cpuinitdata cycles_t last_tsc;
static __cpuinitdata cycles_t max_warp;
static __cpuinitdata int nr_warps;
/*
* TSC-warp measurement loop running on both CPUs:
*/
static __cpuinit void check_tsc_warp(void)
{
cycles_t start, now, prev, end;
int i;
rdtsc_barrier();
start = get_cycles();
rdtsc_barrier();
/*
* The measurement runs for 20 msecs:
*/
end = start + tsc_khz * 20ULL;
now = start;
for (i = 0; ; i++) {
/*
* We take the global lock, measure TSC, save the
* previous TSC that was measured (possibly on
* another CPU) and update the previous TSC timestamp.
*/
__raw_spin_lock(&sync_lock);
prev = last_tsc;
rdtsc_barrier();
now = get_cycles();
rdtsc_barrier();
last_tsc = now;
__raw_spin_unlock(&sync_lock);
/*
* Be nice every now and then (and also check whether
* measurement is done [we also insert a 10 million
* loops safety exit, so we dont lock up in case the
* TSC readout is totally broken]):
*/
if (unlikely(!(i & 7))) {
if (now > end || i > 10000000)
break;
cpu_relax();
touch_nmi_watchdog();
}
/*
* Outside the critical section we can now see whether
* we saw a time-warp of the TSC going backwards:
*/
if (unlikely(prev > now)) {
__raw_spin_lock(&sync_lock);
max_warp = max(max_warp, prev - now);
nr_warps++;
__raw_spin_unlock(&sync_lock);
}
}
WARN(!(now-start),
"Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
now-start, end-start);
}
/*
* Source CPU calls into this - it waits for the freshly booted
* target CPU to arrive and then starts the measurement:
*/
void __cpuinit check_tsc_sync_source(int cpu)
{
int cpus = 2;
/*
* No need to check if we already know that the TSC is not
* synchronized:
*/
if (unsynchronized_tsc())
return;
if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
printk(KERN_INFO
"Skipping synchronization checks as TSC is reliable.\n");
return;
}
printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:",
smp_processor_id(), cpu);
/*
* Reset it - in case this is a second bootup:
*/
atomic_set(&stop_count, 0);
/*
* Wait for the target to arrive:
*/
while (atomic_read(&start_count) != cpus-1)
cpu_relax();
/*
* Trigger the target to continue into the measurement too:
*/
atomic_inc(&start_count);
check_tsc_warp();
while (atomic_read(&stop_count) != cpus-1)
cpu_relax();
if (nr_warps) {
printk("\n");
printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
" turning off TSC clock.\n", max_warp);
mark_tsc_unstable("check_tsc_sync_source failed");
} else {
printk(" passed.\n");
}
x86: fix: s2ram + P4 + tsc = annoyance s2ram recently became useful here, except for the kernel's annoying habit of disabling my P4's perfectly good TSC. [ 107.894470] CPU 1 is now offline [ 107.894474] SMP alternatives: switching to UP code [ 107.895832] CPU0 attaching sched-domain: [ 107.895836] domain 0: span 1 [ 107.895838] groups: 1 [ 107.896097] CPU1 is down [ 3.726156] Intel machine check architecture supported. [ 3.726165] Intel machine check reporting enabled on CPU#0. [ 3.726167] CPU0: Intel P4/Xeon Extended MCE MSRs (12) available [ 3.726170] CPU0: Thermal monitoring enabled [ 3.726175] Back to C! [ 3.726708] Force enabled HPET at resume [ 3.726775] Enabling non-boot CPUs ... [ 3.727049] CPU0 attaching NULL sched-domain. [ 3.727165] SMP alternatives: switching to SMP code [ 3.727858] Booting processor 1/1 eip 3000 [ 3.727862] CPU 1 irqstacks, hard=b042f000 soft=b042d000 [ 3.738173] Initializing CPU#1 [ 3.798912] Calibrating delay using timer specific routine.. 5986.12 BogoMIPS (lpj=2993061) [ 3.798920] CPU: After generic identify, caps: bfebfbff 00000000 00000000 00000000 00004400 00000000 00000000 00000000 [ 3.798931] CPU: Trace cache: 12K uops, L1 D cache: 8K [ 3.798934] CPU: L2 cache: 512K [ 3.798936] CPU: Physical Processor ID: 0 [ 3.798938] CPU: After all inits, caps: bfebfbff 00000000 00000000 0000b080 00004400 00000000 00000000 00000000 [ 3.798946] Intel machine check architecture supported. [ 3.798952] Intel machine check reporting enabled on CPU#1. [ 3.798955] CPU1: Intel P4/Xeon Extended MCE MSRs (12) available [ 3.798959] CPU1: Thermal monitoring enabled [ 3.799161] CPU1: Intel(R) Pentium(R) 4 CPU 3.00GHz stepping 09 [ 3.799187] checking TSC synchronization [CPU#0 -> CPU#1]: [ 3.819181] Measured 63588552840 cycles TSC warp between CPUs, turning off TSC clock. [ 3.819184] Marking TSC unstable due to: check_tsc_sync_source failed. If check_tsc_warp() is called after initial boot, and the TSC has in the meantime been set (BIOS, user, silicon, elves) to a value lower than the last stored/stale value, we blame the TSC. Reset to pristine condition after every test. Signed-off-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-01-30 12:30:04 +00:00
/*
* Reset it - just in case we boot another CPU later:
*/
atomic_set(&start_count, 0);
nr_warps = 0;
max_warp = 0;
last_tsc = 0;
/*
* Let the target continue with the bootup:
*/
atomic_inc(&stop_count);
}
/*
* Freshly booted CPUs call into this:
*/
void __cpuinit check_tsc_sync_target(void)
{
int cpus = 2;
if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
return;
/*
* Register this CPU's participation and wait for the
* source CPU to start the measurement:
*/
atomic_inc(&start_count);
while (atomic_read(&start_count) != cpus)
cpu_relax();
check_tsc_warp();
/*
* Ok, we are done:
*/
atomic_inc(&stop_count);
/*
* Wait for the source CPU to print stuff:
*/
while (atomic_read(&stop_count) != cpus)
cpu_relax();
}
#undef NR_LOOPS