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_xscale.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/arm/kernel/perf_event_xscale.c') diff --git a/arch/arm/kernel/perf_event_xscale.c b/arch/arm/kernel/perf_event_xscale.c index 28cd3b025bc3..39affbe4fdb2 100644 --- a/arch/arm/kernel/perf_event_xscale.c +++ b/arch/arm/kernel/perf_event_xscale.c @@ -246,7 +246,7 @@ xscale1pmu_handle_irq(int irq_num, void *dev) continue; hwc = &event->hw; - armpmu_event_update(event, hwc, idx); + armpmu_event_update(event, hwc, idx, 1); data.period = event->hw.last_period; if (!armpmu_event_set_period(event, hwc, idx)) continue; @@ -578,7 +578,7 @@ xscale2pmu_handle_irq(int irq_num, void *dev) continue; hwc = &event->hw; - armpmu_event_update(event, hwc, idx); + armpmu_event_update(event, hwc, idx, 1); data.period = event->hw.last_period; if (!armpmu_event_set_period(event, hwc, idx)) continue; -- cgit