This Linux kernel change "MIPS, Perf-events: Use unsigned delta for right shift in event update" is included in the Linux 2.6.38 release. This change is authored by Deng-Cheng Zhu <dengcheng.zhu [at] gmail.com> on Fri Jan 21 16:19:21 2011 +0800. The commit for this change in Linux stable tree is ba9786f (patch).
MIPS, Perf-events: Use unsigned delta for right shift in event update Leverage the commit for ARM by Will Deacon: - 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. Acked-by: Will Deacon <[email protected]> Acked-by: David Daney <[email protected]> Signed-off-by: Deng-Cheng Zhu <[email protected]> To: [email protected] To: [email protected] To: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Patchwork: http://patchwork.linux-mips.org/patch/2015/ Signed-off-by: Ralf Baechle <[email protected]>
There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.
arch/mips/kernel/perf_event.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/mips/kernel/perf_event.c b/arch/mips/kernel/perf_event.c index 8f7d2f8..a824485 100644 --- a/arch/mips/kernel/perf_event.c +++ b/arch/mips/kernel/perf_event.c @@ -169,7 +169,7 @@ static void mipspmu_event_update(struct perf_event *event, unsigned long flags; int shift = 64 - TOTAL_BITS; s64 prev_raw_count, new_raw_count; - s64 delta; + u64 delta; again: prev_raw_count = local64_read(&hwc->prev_count);