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| author | Will Deacon <will.deacon@arm.com> | 2010-07-02 19:41:52 +0400 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2010-07-05 02:11:37 +0400 |
| commit | 446a5a8b1eb91a6990e5c8fe29f14e7a95b69132 (patch) | |
| tree | dd60d5a5db4438d66e0baa78acda85f7be4fbae6 /arch | |
| parent | 42c4dafe803dcad82980fd8b0831a89032156f93 (diff) | |
| download | linux-446a5a8b1eb91a6990e5c8fe29f14e7a95b69132.tar.xz | |
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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm/kernel/perf_event.c | 2 |
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; again: prev_raw_count = atomic64_read(&hwc->prev_count); |