From 53c37c17aafcf50f7c6fddaf01dda8f9d7e31ddf Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 12 May 2008 21:20:46 +0200 Subject: ftrace: fast, scalable, synchronized timestamps implement globally synchronized, fast and scalable time source for tracing. Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- kernel/trace/trace.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 53 insertions(+), 1 deletion(-) 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; -- cgit v1.2.3