From bd2b5b12849a3446abad0b25e920f86f5480b309 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 10 Jun 2009 13:40:57 +0200 Subject: perf_counter: More aggressive frequency adjustment Also employ the overflow handler to adjust the frequency, this results in a stable frequency in about 40~50 samples, instead of that many ticks. This also means we can start sampling at a sample period of 1 without running head-first into the throttle. It relies on sched_clock() to accurately measure the time difference between the overflow NMIs. Signed-off-by: Peter Zijlstra Cc: Mike Galbraith Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo LKML-Reference: Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_counter.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c index 49f258537cb..240ca563063 100644 --- a/arch/x86/kernel/cpu/perf_counter.c +++ b/arch/x86/kernel/cpu/perf_counter.c @@ -696,10 +696,11 @@ static int __hw_perf_counter_init(struct perf_counter *counter) if (!attr->exclude_kernel) hwc->config |= ARCH_PERFMON_EVENTSEL_OS; - if (!hwc->sample_period) + if (!hwc->sample_period) { hwc->sample_period = x86_pmu.max_period; + atomic64_set(&hwc->period_left, hwc->sample_period); + } - atomic64_set(&hwc->period_left, hwc->sample_period); counter->destroy = hw_perf_counter_destroy; /* -- cgit v1.2.3-70-g09d2