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ftrace: fast, scalable, synchronized timestamps

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implement globally synchronized, fast and scalable time source for tracing.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Ingo Molnar 2008-05-12 21:20:46 +02:00 committed by Thomas Gleixner
parent 750ed1a407
commit 53c37c17aa
1 changed files with 53 additions and 1 deletions
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54
kernel/trace/trace.c
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@ -42,9 +42,61 @@ ns2usecs(cycle_t nsec)
return nsec;
}
static const int time_sync_freq_max = 128;
static const cycle_t time_sync_thresh = 100000;
static DEFINE_PER_CPU(cycle_t, time_offset);
static DEFINE_PER_CPU(cycle_t, prev_cpu_time);
static DEFINE_PER_CPU(int, time_sync_count);
static DEFINE_PER_CPU(int, time_sync_freq);
/*
* Global lock which we take every now and then to synchronize
* the CPUs time. This method is not warp-safe, but it's good
* enough to synchronize slowly diverging time sources and thus
* it's good enough for tracing:
*/
static DEFINE_SPINLOCK(time_sync_lock);
static cycle_t prev_global_time;
static notrace cycle_t __ftrace_now_sync(cycles_t time, int cpu)
{
unsigned long flags;
spin_lock_irqsave(&time_sync_lock, flags);
/*
* Update the synchronization frequency:
*/
if (per_cpu(time_sync_freq, cpu) < time_sync_freq_max)
per_cpu(time_sync_freq, cpu) *= 2;
per_cpu(time_sync_count, cpu) = per_cpu(time_sync_freq, cpu);
if (time < prev_global_time) {
per_cpu(time_offset, cpu) += prev_global_time - time;
time = prev_global_time;
} else {
prev_global_time = time;
}
spin_unlock_irqrestore(&time_sync_lock, flags);
return time;
}
notrace cycle_t ftrace_now(int cpu)
{
return cpu_clock(cpu);
cycle_t prev_cpu_time, time, delta_time;
prev_cpu_time = per_cpu(prev_cpu_time, cpu);
time = sched_clock() + per_cpu(time_offset, cpu);
delta_time = time-prev_cpu_time;
if (unlikely(delta_time > time_sync_thresh ||
--per_cpu(time_sync_count, cpu) <= 0))
time = __ftrace_now_sync(time, cpu);
return time;
}
static atomic_t tracer_counter;