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author | Ingo Molnar <mingo@elte.hu> | 2008-05-12 21:20:46 +0200 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2008-05-23 20:42:41 +0200 |
commit | 53c37c17aafcf50f7c6fddaf01dda8f9d7e31ddf (patch) | |
tree | 69d04219218c263d43da88068342a4c91a757877 | |
parent | 750ed1a40783432d0dcb0e6c2e813a12615d7664 (diff) | |
download | linux-53c37c17aafcf50f7c6fddaf01dda8f9d7e31ddf.tar.bz2 |
ftrace: fast, scalable, synchronized timestamps
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>
-rw-r--r-- | kernel/trace/trace.c | 54 |
1 files changed, 53 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index e3778ab0d3f7..9a931c7c2da3 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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; |