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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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19
arch/arm/kernel/perf_event.c
View file

@ -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;
}
}

2
arch/arm/kernel/perf_event_v6.c
View file

@ -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;

2
arch/arm/kernel/perf_event_v7.c
View file

@ -782,7 +782,7 @@ static irqreturn_t armv7pmu_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;

4
arch/arm/kernel/perf_event_xscale.c
View file

@ -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;