linux-kernel - [PATCH v2] perf record/arm-spe: Override attr->sample

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Message-Id: <20220118144054.2541-1-german.gomez@arm.com>
Date:   Tue, 18 Jan 2022 14:40:54 +0000
From:   German Gomez <german.gomez@....com>
To:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Cc:     German Gomez <german.gomez@....com>,
        Chase Conklin <chase.conklin@....com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Stephane Eranian <eranian@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: [PATCH v2] perf record/arm-spe: Override attr->sample_period for non-libpfm4 events

A previous patch preventing "attr->sample_period" values from being
overridden in pfm events changed a related behaviour in arm-spe.

Before said patch:
perf record -c 10000 -e arm_spe_0// -- sleep 1

Would yield an SPE event with period=10000. After the patch, the period
in "-c 10000" was being ignored because the arm-spe code initializes
sample_period to a non-zero value.

This patch restores the previous behaviour for non-libpfm4 events.

Reported-by: Chase Conklin <chase.conklin@....com>
Fixes: ae5dcc8abe31 (“perf record: Prevent override of attr->sample_period for libpfm4 events”)
Signed-off-by: German Gomez <german.gomez@....com>
---
As suggested by Arnaldo, this v2 doesn't include a test in order to not
block this fix for longer than necessary. So the test can be sent as a
separate submission later.

Changes since v1.
 - Update commit message (James Clark)
---
 tools/perf/util/evsel.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a59fb2ecb84e..86ab038f020f 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1065,6 +1065,17 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un
 {
 }
 
+static void evsel__set_default_freq_period(struct record_opts *opts,
+					   struct perf_event_attr *attr)
+{
+	if (opts->freq) {
+		attr->freq = 1;
+		attr->sample_freq = opts->freq;
+	} else {
+		attr->sample_period = opts->default_interval;
+	}
+}
+
 /*
  * The enable_on_exec/disabled value strategy:
  *
@@ -1131,14 +1142,12 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
 	 * We default some events to have a default interval. But keep
 	 * it a weak assumption overridable by the user.
 	 */
-	if (!attr->sample_period) {
-		if (opts->freq) {
-			attr->freq		= 1;
-			attr->sample_freq	= opts->freq;
-		} else {
-			attr->sample_period = opts->default_interval;
-		}
-	}
+	if ((evsel->is_libpfm_event && !attr->sample_period) ||
+	    (!evsel->is_libpfm_event && (!attr->sample_period ||
+					 opts->user_freq != UINT_MAX ||
+					 opts->user_interval != ULLONG_MAX)))
+		evsel__set_default_freq_period(opts, attr);
+
 	/*
 	 * If attr->freq was set (here or earlier), ask for period
 	 * to be sampled.
-- 
2.25.1