From: Stephane Eranian eranian@google.com
[ Upstream commit fc17db8aa4c53cbd2d5469bb0521ea0f0a6dbb27 ]
The kernel cannot disambiguate when 2+ PEBS counters overflow at the same time. This is what the comment for this code suggests. However, I see the comparison is done with the unfiltered p->status which is a copy of IA32_PERF_GLOBAL_STATUS at the time of the sample. This register contains more than the PEBS counter overflow bits. It also includes many other bits which could also be set.
Signed-off-by: Namhyung Kim namhyung@kernel.org Signed-off-by: Stephane Eranian eranian@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20201126110922.317681-2-namhyung@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/events/intel/ds.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c index 1aaba2c8a9ba6..eb8bd0eeace7d 100644 --- a/arch/x86/events/intel/ds.c +++ b/arch/x86/events/intel/ds.c @@ -1912,7 +1912,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs) * that caused the PEBS record. It's called collision. * If collision happened, the record will be dropped. */ - if (p->status != (1ULL << bit)) { + if (pebs_status != (1ULL << bit)) { for_each_set_bit(i, (unsigned long *)&pebs_status, size) error[i]++; continue;