Within the read syscall we update the event count via
pmu->read callback if the event is in ACTIVE state.
This triggers event update (x86_perf_event_update) for
x86 pmu and leads to wrong event count in case the event
hasn't been started yet -> the event base is not adjusted
to new cpu and new count computation is based on previous
CPU prev_count.
Fixing this to update the counter only if it has been
started, so the event base is properly adjusted.
Signed-off-by: Jiri Olsa <jo...@redhat.com>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: Corey Ashford <cjash...@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Ingo Molnar <mi...@elte.hu>
Cc: Paul Mackerras <pau...@samba.org>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
---
arch/x86/kernel/cpu/perf_event.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 8355c84..e89c773 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1570,7 +1570,11 @@ early_initcall(init_hw_perf_events);
static inline void x86_pmu_read(struct perf_event *event)
{
- x86_perf_event_update(event);
+ struct hw_perf_event *hwc = &event->hw;
+
+ /* Update only if the event has already been started. */
+ if (!(hwc->state & PERF_HES_ARCH))
+ x86_perf_event_update(event);
}
/*
--
1.7.11.7
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