From dc853e26f73e903e0c87e24f2695b5dcf33b3bc1 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Fri, 14 Jul 2017 18:35:51 +0200 Subject: [PATCH] perf/x86/intel: Fix debug_store reset field for freq events There's a bug in PEBs event enabling code, that prevents PEBS freq events to work properly after non freq PEBS event was run. freq events - perf_event_attr::freq set -F option of perf record PEBS events - perf_event_attr::precise_ip > 0 default for perf record Like in following example with CPU 0 busy, we expect ~10000 samples for following perf tool run: # perf record -F 10000 -C 0 sleep 1 [ perf record: Woken up 2 times to write data ] [ perf record: Captured and wrote 0.640 MB perf.data (10031 samples) ] Everything's fine, but once we run non freq PEBS event like: # perf record -c 10000 -C 0 sleep 1 [ perf record: Woken up 4 times to write data ] [ perf record: Captured and wrote 1.053 MB perf.data (20061 samples) ] the freq events start to fail like this: # perf record -F 10000 -C 0 sleep 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.185 MB perf.data (40 samples) ] The issue is in non freq PEBs event initialization of debug_store reset field, which value is used to auto-reload the counter value after PEBS event drain. This value is not being used for PEBS freq events, but once we run non freq event it stays in debug_store data and screws the sample_freq counting for PEBS freq events. Setting the reset field to 0 for freq events. Signed-off-by: Jiri Olsa Acked-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Kan Liang Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170714163551.19459-1-jolsa@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/events/intel/ds.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 2ca4d2d7b5fc..6dc8a59e1bfb 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -895,6 +895,8 @@ void intel_pmu_pebs_enable(struct perf_event *event) if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) { ds->pebs_event_reset[hwc->idx] = (u64)(-hwc->sample_period) & x86_pmu.cntval_mask; + } else { + ds->pebs_event_reset[hwc->idx] = 0; } } -- 2.20.1