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ARM: 6835/1: perf: ensure overflows aren't missed due to IRQ latency

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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 <jamie@jamieiles.com>
Reported-by: Ashwin Chaugule <ashwinc@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Will Deacon
2011-03-25 17:12:37 +01:00
committed by Russell King
parent 574b69cbb6
commit a737823d37
4 changed files with 15 additions and 12 deletions
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2
arch/arm/kernel/perf_event_v6.c
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@@ -474,7 +474,7 @@ armv6pmu_handle_irq(int irq_num,
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;