linux-kernel - [tip: perf/urgent] perf/x86/intel: Check PEBS status correctly

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Message-ID: <160698645173.3364.15000684811253542109.tip-bot2@tip-bot2>
Date:   Thu, 03 Dec 2020 09:07:31 -0000
From:   "tip-bot2 for Stephane Eranian" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/intel: Check PEBS status correctly

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     fc17db8aa4c53cbd2d5469bb0521ea0f0a6dbb27
Gitweb:        https://git.kernel.org/tip/fc17db8aa4c53cbd2d5469bb0521ea0f0a6dbb27
Author:        Stephane Eranian <eranian@...gle.com>
AuthorDate:    Thu, 26 Nov 2020 20:09:22 +09:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 03 Dec 2020 10:00:26 +01:00

perf/x86/intel: Check PEBS status correctly

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@...nel.org>
Signed-off-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20201126110922.317681-2-namhyung@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 89dba58..485c506 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1916,7 +1916,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs, struct perf_sample_d
 		 * 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;