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

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Message-ID: <172052531604.2215.3507740369226432766.tip-bot2@tip-bot2>
Date: Tue, 09 Jul 2024 11:41:56 -0000
From: "tip-bot2 for Kan Liang" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Bayduraev, Alexey V" <alexey.v.bayduraev@...el.com>,
 Kan Liang <kan.liang@...ux.intel.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, stable@...r.kernel.org,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: perf/core] perf/x86/intel/ds: Fix non 0 retire latency on Raptorlake

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

Commit-ID:     e5f32ad56b22ebe384a6e7ddad6e9520c5495563
Gitweb:        https://git.kernel.org/tip/e5f32ad56b22ebe384a6e7ddad6e9520c5495563
Author:        Kan Liang <kan.liang@...ux.intel.com>
AuthorDate:    Mon, 08 Jul 2024 12:33:36 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 09 Jul 2024 13:26:39 +02:00

perf/x86/intel/ds: Fix non 0 retire latency on Raptorlake

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>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: "Bayduraev, Alexey V" <alexey.v.bayduraev@...el.com>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20240708193336.1192217-4-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 b9cc520..fa5ea65 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1944,8 +1944,12 @@ 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