linux-kernel - [tip: perf/core] perf/x86/intel/pebs: Fix PEBS timestamps overwritten

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Date:   Tue, 06 Sep 2022 09:41:33 -0000
From:   "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andreas Kogler <andreas.kogler.0x@...il.com>,
        Stephane Eranian <eranian@...gle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf/x86/intel/pebs: Fix PEBS timestamps overwritten

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

Commit-ID:     47a3aeb39e8dc099ae431cd8b46bdf218f5511b2
Gitweb:        https://git.kernel.org/tip/47a3aeb39e8dc099ae431cd8b46bdf218f5511b2
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Thu, 01 Sep 2022 06:09:55 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 06 Sep 2022 11:33:01 +02:00

perf/x86/intel/pebs: Fix PEBS timestamps overwritten

The PEBS TSC-based timestamps do not appear correctly in the final
perf.data output file from perf record.

The data->time field setup by PEBS in the setup_pebs_fixed_sample_data()
is later overwritten by perf_events generic code in
perf_prepare_sample(). There is an ordering problem.

Set the sample flags when the data->time is updated by PEBS.
The data->time field will not be overwritten anymore.

Reported-by: Andreas Kogler <andreas.kogler.0x@...il.com>
Reported-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20220901130959.1285717-3-kan.liang@linux.intel.com
---
 arch/x86/events/intel/ds.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index ba60427..cdd857b 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1635,8 +1635,10 @@ static void setup_pebs_fixed_sample_data(struct perf_event *event,
 	 * We can only do this for the default trace clock.
 	 */
 	if (x86_pmu.intel_cap.pebs_format >= 3 &&
-		event->attr.use_clockid == 0)
+		event->attr.use_clockid == 0) {
 		data->time = native_sched_clock_from_tsc(pebs->tsc);
+		data->sample_flags |= PERF_SAMPLE_TIME;
+	}
 
 	if (has_branch_stack(event))
 		data->br_stack = &cpuc->lbr_stack;
@@ -1697,8 +1699,10 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
 	perf_sample_data_init(data, 0, event->hw.last_period);
 	data->period = event->hw.last_period;
 
-	if (event->attr.use_clockid == 0)
+	if (event->attr.use_clockid == 0) {
 		data->time = native_sched_clock_from_tsc(basic->tsc);
+		data->sample_flags |= PERF_SAMPLE_TIME;
+	}
 
 	/*
 	 * We must however always use iregs for the unwinder to stay sane; the