linux-kernel - [PATCH] perf/x86/intel/ds: Fix non 0 retire latency on Raptorlake

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Date: Fri,  5 Apr 2024 07:30:32 -0700
From: kan.liang@...ux.intel.com
To: peterz@...radead.org,
	mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com,
	linux-kernel@...r.kernel.org
Cc: Kan Liang <kan.liang@...ux.intel.com>,
	"Bayduraev, Alexey V" <alexey.v.bayduraev@...el.com>,
	stable@...r.kernel.org
Subject: [PATCH] perf/x86/intel/ds: Fix non 0 retire latency on Raptorlake

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

A non-0 retire latency can be observed on a Raptorlake which doesn't
support the retire latency feature.
By design, the retire latency shares the PERF_SAMPLE_WEIGHT_STRUCT
sample type with other types of latency. That could avoid adding too
many different sample types to support all kinds of latency. For the
machine which doesn't support some kind of latency, 0 should be
returned.

Perf doesn’t clear/init all the fields of a sample data for the sake
of performance. It expects the later perf_{prepare,output}_sample() to
update the uninitialized field. However, the current implementation
doesn't touch the field of the retire latency if the feature is not
supported. The memory garbage is dumped into the perf data.

Clear the retire latency if the feature is not supported.

Fixes: c87a31093c70 ("perf/x86: Support Retire Latency")
Reported-by: "Bayduraev, Alexey V" <alexey.v.bayduraev@...el.com>
Tested-by: "Bayduraev, Alexey V" <alexey.v.bayduraev@...el.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Cc: stable@...r.kernel.org
---
 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 f95cca6b632a..838f3e23bce9 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1989,8 +1989,12 @@ static void setup_pebs_adaptive_sample_data(struct perf_event *event,
 	set_linear_ip(regs, basic->ip);
 	regs->flags = PERF_EFLAGS_EXACT;

-	if ((sample_type & PERF_SAMPLE_WEIGHT_STRUCT) && (x86_pmu.flags & PMU_FL_RETIRE_LATENCY))
-		data->weight.var3_w = format_size >> PEBS_RETIRE_LATENCY_OFFSET & PEBS_LATENCY_MASK;
+	if (sample_type & PERF_SAMPLE_WEIGHT_STRUCT) {
+		if (x86_pmu.flags & PMU_FL_RETIRE_LATENCY)
+			data->weight.var3_w = format_size >> PEBS_RETIRE_LATENCY_OFFSET & PEBS_LATENCY_MASK;
+		else
+			data->weight.var3_w = 0;
+	}

 	/*
 	 * The record for MEMINFO is in front of GP
-- 
2.35.1