From a737823d37666255e3e74ce84bc9611a038e0888 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 25 Mar 2011 17:12:37 +0100 Subject: ARM: 6835/1: perf: ensure overflows aren't missed due to IRQ latency If a counter overflows during a perf stat profiling run it may overtake the last known value of the counter: 0 prev new 0xffffffff |----------|-------|----------------------| In this case, the number of events that have occurred is (0xffffffff - prev) + new. Unfortunately, the event update code will not realise an overflow has occurred and will instead report the event delta as (new - prev) which may be considerably smaller than the real count. This patch adds an extra argument to armpmu_event_update which indicates whether or not an overflow has occurred. If an overflow has occurred then we use the maximum period of the counter to calculate the elapsed events. Acked-by: Jamie Iles Reported-by: Ashwin Chaugule Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/kernel/perf_event.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) (limited to 'arch/arm/kernel/perf_event.c') diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index e422f4c269a0..69cfee0fe00f 100644 --- a/arch/arm/kernel/perf_event.c +++ b/arch/arm/kernel/perf_event.c @@ -205,11 +205,9 @@ armpmu_event_set_period(struct perf_event *event, static u64 armpmu_event_update(struct perf_event *event, struct hw_perf_event *hwc, - int idx) + int idx, int overflow) { - int shift = 64 - 32; - s64 prev_raw_count, new_raw_count; - u64 delta; + u64 delta, prev_raw_count, new_raw_count; again: prev_raw_count = local64_read(&hwc->prev_count); @@ -219,8 +217,13 @@ again: new_raw_count) != prev_raw_count) goto again; - delta = (new_raw_count << shift) - (prev_raw_count << shift); - delta >>= shift; + new_raw_count &= armpmu->max_period; + prev_raw_count &= armpmu->max_period; + + if (overflow) + delta = armpmu->max_period - prev_raw_count + new_raw_count; + else + delta = new_raw_count - prev_raw_count; local64_add(delta, &event->count); local64_sub(delta, &hwc->period_left); @@ -237,7 +240,7 @@ armpmu_read(struct perf_event *event) if (hwc->idx < 0) return; - armpmu_event_update(event, hwc, hwc->idx); + armpmu_event_update(event, hwc, hwc->idx, 0); } static void @@ -255,7 +258,7 @@ armpmu_stop(struct perf_event *event, int flags) if (!(hwc->state & PERF_HES_STOPPED)) { armpmu->disable(hwc, hwc->idx); barrier(); /* why? */ - armpmu_event_update(event, hwc, hwc->idx); + armpmu_event_update(event, hwc, hwc->idx, 0); hwc->state |= PERF_HES_STOPPED | PERF_HES_UPTODATE; } } -- cgit v1.2.3-55-g7522