From: Will Deacon Date: Fri, 2 Jul 2010 15:41:52 +0000 (+0100) Subject: ARM: 6205/1: perf: ensure counter delta is treated as unsigned X-Git-Tag: v2.6.35-rc4~1^2 X-Git-Url: https://bbs.cooldavid.org/git/?p=net-next-2.6.git;a=commitdiff_plain;h=446a5a8b1eb91a6990e5c8fe29f14e7a95b69132 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: Acked-by: Jamie Iles Signed-off-by: Will Deacon Signed-off-by: Russell King --- diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index c45768614c8..de12536d687 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);