linux-kernel - [PATCH 2/6] perf/x86/intel/pebs: Fix PEBS timestamps overwritten

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Date:   Wed, 31 Aug 2022 07:55:10 -0700
From:   kan.liang@...ux.intel.com
To:     peterz@...radead.org, acme@...nel.org, mingo@...hat.com,
        eranian@...gle.com, mpe@...erman.id.au,
        linux-kernel@...r.kernel.org
Cc:     ak@...ux.intel.com, andreas.kogler.0x@...il.com,
        atrajeev@...ux.vnet.ibm.com, Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH 2/6] perf/x86/intel/pebs: Fix PEBS timestamps overwritten

From: Kan Liang <kan.liang@...ux.intel.com>

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>
---
 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 6ce73b4ae2f3..3af24c4891fb 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1640,8 +1640,10 @@ 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;
@@ -1702,8 +1704,10 @@ 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
-- 
2.35.1