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authorWill Deacon <will.deacon@arm.com>2012-03-06 17:33:17 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2012-03-07 09:40:48 +0000
commit5727347180ebc6b4a866fcbe00dcb39cc03acb37 (patch)
treeed27e4b37407917d2f9813a4684cceb64f0d6f93 /arch/arm/kernel/perf_event_v7.c
parent81caaf2503be8fbb738ea4f124063dcc24958397 (diff)
downloadvexpress-lsk-5727347180ebc6b4a866fcbe00dcb39cc03acb37.tar.gz
ARM: 7354/1: perf: limit sample_period to half max_period in non-sampling mode
On ARM, the PMU does not stop counting after an overflow and therefore IRQ latency affects the new counter value read by the kernel. This is significant for non-sampling runs where it is possible for the new value to overtake the previous one, causing the delta to be out by up to max_period events. Commit a737823d ("ARM: 6835/1: perf: ensure overflows aren't missed due to IRQ latency") attempted to fix this problem by allowing interrupt handlers to pass an overflow flag to the event update function, causing the overflow calculation to assume that the counter passed through zero when going from prev to new. Unfortunately, this doesn't work when overflow occurs on the perf_task_tick path because we have the flag cleared and end up computing a large negative delta. This patch removes the overflow flag from armpmu_event_update and instead limits the sample_period to half of the max_period for non-sampling profiling runs. Cc: <stable@vger.kernel.org> Signed-off-by: Ming Lei <ming.lei@canonical.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel/perf_event_v7.c')
-rw-r--r--arch/arm/kernel/perf_event_v7.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
index 6933244c68f..6f488610f8f 100644
--- a/arch/arm/kernel/perf_event_v7.c
+++ b/arch/arm/kernel/perf_event_v7.c
@@ -963,7 +963,7 @@ static irqreturn_t armv7pmu_handle_irq(int irq_num, void *dev)
continue;
hwc = &event->hw;
- armpmu_event_update(event, hwc, idx, 1);
+ armpmu_event_update(event, hwc, idx);
data.period = event->hw.last_period;
if (!armpmu_event_set_period(event, hwc, idx))
continue;