linux/kernel/trace/trace_clock.c

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/*
* tracing clocks
*
* Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Implements 3 trace clock variants, with differing scalability/precision
* tradeoffs:
*
* - local: CPU-local trace clock
* - medium: scalable global clock with some jitter
* - global: globally monotonic, serialized clock
*
* Tracer plugins will chose a default from these clocks.
*/
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/ktime.h>
#include <linux/trace_clock.h>
tracing: do not disable interrupts for trace_clock_local Disabling interrupts in trace_clock_local takes quite a performance hit to the recording of traces. Using perf top we see: ------------------------------------------------------------------------------ PerfTop: 244 irqs/sec kernel:100.0% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 2842.00 - 40.4% : trace_clock_local 1043.00 - 14.8% : rb_reserve_next_event 784.00 - 11.1% : ring_buffer_lock_reserve 600.00 - 8.5% : __rb_reserve_next 579.00 - 8.2% : rb_end_commit 440.00 - 6.3% : ring_buffer_unlock_commit 290.00 - 4.1% : ring_buffer_producer_thread [ring_buffer_benchmark] 155.00 - 2.2% : debug_smp_processor_id 117.00 - 1.7% : trace_recursive_unlock 103.00 - 1.5% : ring_buffer_event_data 28.00 - 0.4% : do_gettimeofday 22.00 - 0.3% : _spin_unlock_irq 14.00 - 0.2% : native_read_tsc 11.00 - 0.2% : getnstimeofday Where trace_clock_local is 40% of the tracing, and the time for recording a trace according to ring_buffer_benchmark is 210ns. After converting the interrupts to preemption disabling we have from perf top: ------------------------------------------------------------------------------ PerfTop: 1084 irqs/sec kernel:99.9% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 1277.00 - 16.8% : native_read_tsc 1148.00 - 15.1% : rb_reserve_next_event 896.00 - 11.8% : ring_buffer_lock_reserve 688.00 - 9.1% : __rb_reserve_next 664.00 - 8.8% : rb_end_commit 563.00 - 7.4% : ring_buffer_unlock_commit 508.00 - 6.7% : _spin_unlock_irq 365.00 - 4.8% : debug_smp_processor_id 321.00 - 4.2% : trace_clock_local 303.00 - 4.0% : ring_buffer_producer_thread [ring_buffer_benchmark] 273.00 - 3.6% : native_sched_clock 122.00 - 1.6% : trace_recursive_unlock 113.00 - 1.5% : sched_clock 101.00 - 1.3% : ring_buffer_event_data 53.00 - 0.7% : tick_nohz_stop_sched_tick Where trace_clock_local drops from 40% to only taking 4% of the total time. The trace time also goes from 210ns down to 179ns (31ns). I talked with Peter Zijlstra about the impact that sched_clock may have without having interrupts disabled, and he told me that if a timer interrupt comes in, sched_clock may report a wrong time. Balancing a seldom incorrect timestamp with a 15% performance boost, I'll take the performance boost. Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-11-12 00:36:03 +00:00
#include "trace.h"
/*
* trace_clock_local(): the simplest and least coherent tracing clock.
*
* Useful for tracing that does not cross to other CPUs nor
* does it go through idle events.
*/
u64 notrace trace_clock_local(void)
{
u64 clock;
tracing: do not disable interrupts for trace_clock_local Disabling interrupts in trace_clock_local takes quite a performance hit to the recording of traces. Using perf top we see: ------------------------------------------------------------------------------ PerfTop: 244 irqs/sec kernel:100.0% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 2842.00 - 40.4% : trace_clock_local 1043.00 - 14.8% : rb_reserve_next_event 784.00 - 11.1% : ring_buffer_lock_reserve 600.00 - 8.5% : __rb_reserve_next 579.00 - 8.2% : rb_end_commit 440.00 - 6.3% : ring_buffer_unlock_commit 290.00 - 4.1% : ring_buffer_producer_thread [ring_buffer_benchmark] 155.00 - 2.2% : debug_smp_processor_id 117.00 - 1.7% : trace_recursive_unlock 103.00 - 1.5% : ring_buffer_event_data 28.00 - 0.4% : do_gettimeofday 22.00 - 0.3% : _spin_unlock_irq 14.00 - 0.2% : native_read_tsc 11.00 - 0.2% : getnstimeofday Where trace_clock_local is 40% of the tracing, and the time for recording a trace according to ring_buffer_benchmark is 210ns. After converting the interrupts to preemption disabling we have from perf top: ------------------------------------------------------------------------------ PerfTop: 1084 irqs/sec kernel:99.9% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 1277.00 - 16.8% : native_read_tsc 1148.00 - 15.1% : rb_reserve_next_event 896.00 - 11.8% : ring_buffer_lock_reserve 688.00 - 9.1% : __rb_reserve_next 664.00 - 8.8% : rb_end_commit 563.00 - 7.4% : ring_buffer_unlock_commit 508.00 - 6.7% : _spin_unlock_irq 365.00 - 4.8% : debug_smp_processor_id 321.00 - 4.2% : trace_clock_local 303.00 - 4.0% : ring_buffer_producer_thread [ring_buffer_benchmark] 273.00 - 3.6% : native_sched_clock 122.00 - 1.6% : trace_recursive_unlock 113.00 - 1.5% : sched_clock 101.00 - 1.3% : ring_buffer_event_data 53.00 - 0.7% : tick_nohz_stop_sched_tick Where trace_clock_local drops from 40% to only taking 4% of the total time. The trace time also goes from 210ns down to 179ns (31ns). I talked with Peter Zijlstra about the impact that sched_clock may have without having interrupts disabled, and he told me that if a timer interrupt comes in, sched_clock may report a wrong time. Balancing a seldom incorrect timestamp with a 15% performance boost, I'll take the performance boost. Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-11-12 00:36:03 +00:00
int resched;
/*
* sched_clock() is an architecture implemented, fast, scalable,
* lockless clock. It is not guaranteed to be coherent across
* CPUs, nor across CPU idle events.
*/
tracing: do not disable interrupts for trace_clock_local Disabling interrupts in trace_clock_local takes quite a performance hit to the recording of traces. Using perf top we see: ------------------------------------------------------------------------------ PerfTop: 244 irqs/sec kernel:100.0% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 2842.00 - 40.4% : trace_clock_local 1043.00 - 14.8% : rb_reserve_next_event 784.00 - 11.1% : ring_buffer_lock_reserve 600.00 - 8.5% : __rb_reserve_next 579.00 - 8.2% : rb_end_commit 440.00 - 6.3% : ring_buffer_unlock_commit 290.00 - 4.1% : ring_buffer_producer_thread [ring_buffer_benchmark] 155.00 - 2.2% : debug_smp_processor_id 117.00 - 1.7% : trace_recursive_unlock 103.00 - 1.5% : ring_buffer_event_data 28.00 - 0.4% : do_gettimeofday 22.00 - 0.3% : _spin_unlock_irq 14.00 - 0.2% : native_read_tsc 11.00 - 0.2% : getnstimeofday Where trace_clock_local is 40% of the tracing, and the time for recording a trace according to ring_buffer_benchmark is 210ns. After converting the interrupts to preemption disabling we have from perf top: ------------------------------------------------------------------------------ PerfTop: 1084 irqs/sec kernel:99.9% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 1277.00 - 16.8% : native_read_tsc 1148.00 - 15.1% : rb_reserve_next_event 896.00 - 11.8% : ring_buffer_lock_reserve 688.00 - 9.1% : __rb_reserve_next 664.00 - 8.8% : rb_end_commit 563.00 - 7.4% : ring_buffer_unlock_commit 508.00 - 6.7% : _spin_unlock_irq 365.00 - 4.8% : debug_smp_processor_id 321.00 - 4.2% : trace_clock_local 303.00 - 4.0% : ring_buffer_producer_thread [ring_buffer_benchmark] 273.00 - 3.6% : native_sched_clock 122.00 - 1.6% : trace_recursive_unlock 113.00 - 1.5% : sched_clock 101.00 - 1.3% : ring_buffer_event_data 53.00 - 0.7% : tick_nohz_stop_sched_tick Where trace_clock_local drops from 40% to only taking 4% of the total time. The trace time also goes from 210ns down to 179ns (31ns). I talked with Peter Zijlstra about the impact that sched_clock may have without having interrupts disabled, and he told me that if a timer interrupt comes in, sched_clock may report a wrong time. Balancing a seldom incorrect timestamp with a 15% performance boost, I'll take the performance boost. Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-11-12 00:36:03 +00:00
resched = ftrace_preempt_disable();
clock = sched_clock();
tracing: do not disable interrupts for trace_clock_local Disabling interrupts in trace_clock_local takes quite a performance hit to the recording of traces. Using perf top we see: ------------------------------------------------------------------------------ PerfTop: 244 irqs/sec kernel:100.0% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 2842.00 - 40.4% : trace_clock_local 1043.00 - 14.8% : rb_reserve_next_event 784.00 - 11.1% : ring_buffer_lock_reserve 600.00 - 8.5% : __rb_reserve_next 579.00 - 8.2% : rb_end_commit 440.00 - 6.3% : ring_buffer_unlock_commit 290.00 - 4.1% : ring_buffer_producer_thread [ring_buffer_benchmark] 155.00 - 2.2% : debug_smp_processor_id 117.00 - 1.7% : trace_recursive_unlock 103.00 - 1.5% : ring_buffer_event_data 28.00 - 0.4% : do_gettimeofday 22.00 - 0.3% : _spin_unlock_irq 14.00 - 0.2% : native_read_tsc 11.00 - 0.2% : getnstimeofday Where trace_clock_local is 40% of the tracing, and the time for recording a trace according to ring_buffer_benchmark is 210ns. After converting the interrupts to preemption disabling we have from perf top: ------------------------------------------------------------------------------ PerfTop: 1084 irqs/sec kernel:99.9% [1000Hz cpu-clock-msecs], (all, 4 CPUs) ------------------------------------------------------------------------------ samples pcnt kernel function _______ _____ _______________ 1277.00 - 16.8% : native_read_tsc 1148.00 - 15.1% : rb_reserve_next_event 896.00 - 11.8% : ring_buffer_lock_reserve 688.00 - 9.1% : __rb_reserve_next 664.00 - 8.8% : rb_end_commit 563.00 - 7.4% : ring_buffer_unlock_commit 508.00 - 6.7% : _spin_unlock_irq 365.00 - 4.8% : debug_smp_processor_id 321.00 - 4.2% : trace_clock_local 303.00 - 4.0% : ring_buffer_producer_thread [ring_buffer_benchmark] 273.00 - 3.6% : native_sched_clock 122.00 - 1.6% : trace_recursive_unlock 113.00 - 1.5% : sched_clock 101.00 - 1.3% : ring_buffer_event_data 53.00 - 0.7% : tick_nohz_stop_sched_tick Where trace_clock_local drops from 40% to only taking 4% of the total time. The trace time also goes from 210ns down to 179ns (31ns). I talked with Peter Zijlstra about the impact that sched_clock may have without having interrupts disabled, and he told me that if a timer interrupt comes in, sched_clock may report a wrong time. Balancing a seldom incorrect timestamp with a 15% performance boost, I'll take the performance boost. Acked-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-11-12 00:36:03 +00:00
ftrace_preempt_enable(resched);
return clock;
}
/*
* trace_clock(): 'inbetween' trace clock. Not completely serialized,
* but not completely incorrect when crossing CPUs either.
*
* This is based on cpu_clock(), which will allow at most ~1 jiffy of
* jitter between CPUs. So it's a pretty scalable clock, but there
* can be offsets in the trace data.
*/
u64 notrace trace_clock(void)
{
return cpu_clock(raw_smp_processor_id());
}
/*
* trace_clock_global(): special globally coherent trace clock
*
* It has higher overhead than the other trace clocks but is still
* an order of magnitude faster than GTOD derived hardware clocks.
*
* Used by plugins that need globally coherent timestamps.
*/
/* keep prev_time and lock in the same cacheline. */
static struct {
u64 prev_time;
arch_spinlock_t lock;
} trace_clock_struct ____cacheline_aligned_in_smp =
{
.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
};
u64 notrace trace_clock_global(void)
{
unsigned long flags;
int this_cpu;
u64 now;
local_irq_save(flags);
this_cpu = raw_smp_processor_id();
now = cpu_clock(this_cpu);
/*
* If in an NMI context then dont risk lockups and return the
* cpu_clock() time:
*/
if (unlikely(in_nmi()))
goto out;
arch_spin_lock(&trace_clock_struct.lock);
/*
* TODO: if this happens often then maybe we should reset
* my_scd->clock to prev_time+1, to make sure
* we start ticking with the local clock from now on?
*/
if ((s64)(now - trace_clock_struct.prev_time) < 0)
now = trace_clock_struct.prev_time + 1;
trace_clock_struct.prev_time = now;
arch_spin_unlock(&trace_clock_struct.lock);
out:
local_irq_restore(flags);
return now;
}