diff options
authorWill Deacon <will.deacon@arm.com>2010-07-02 16:41:52 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-07-04 23:11:37 +0100
commit446a5a8b1eb91a6990e5c8fe29f14e7a95b69132 (patch)
parent42c4dafe803dcad82980fd8b0831a89032156f93 (diff)
ARM: 6205/1: perf: ensure counter delta is treated as unsigned
Hardware performance counters on ARM are 32-bits wide but atomic64_t variables are used to represent counter data in the hw_perf_event structure. The armpmu_event_update function right-shifts a signed 64-bit delta variable and adds the result to the event count. This can lead to shifting in sign-bits if the MSB of the 32-bit counter value is set. This results in perf output such as: Performance counter stats for 'sleep 20': 18446744073460670464 cycles <-- 0xFFFFFFFFF12A6000 7783773 instructions # 0.000 IPC 465 context-switches 161 page-faults 1172393 branches 20.154242147 seconds time elapsed This patch ensures that the delta value is treated as unsigned so that the right shift sets the upper bits to zero. Cc: <stable@kernel.org> Acked-by: Jamie Iles <jamie.iles@picochip.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index c45768614c8a..de12536d687f 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -201,7 +201,7 @@ armpmu_event_update(struct perf_event *event,
int shift = 64 - 32;
s64 prev_raw_count, new_raw_count;
- s64 delta;
+ u64 delta;
prev_raw_count = atomic64_read(&hwc->prev_count);

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