linux-kernel - [PATCH v2 06/12] perf parse-events: Always track user config changes

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Message-Id: <20251208-james-perf-config-bits-v2-6-4ac0281993b0@linaro.org>
Date: Mon, 08 Dec 2025 14:22:09 +0000
From: James Clark <james.clark@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Arnaldo Carvalho de Melo <acme@...nel.org>, 
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
 Adrian Hunter <adrian.hunter@...el.com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Mike Leach <mike.leach@...aro.org>, John Garry <john.g.garry@...cle.com>, 
 Will Deacon <will@...nel.org>, Leo Yan <leo.yan@...ux.dev>, leo.yan@....com
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
 James Clark <james.clark@...aro.org>
Subject: [PATCH v2 06/12] perf parse-events: Always track user config
 changes

Requiring the 'pmu->perf_event_attr_init_default' callback to be set to
track user changes is a bit of a trap to fall in. It's hard to see that
this is required when depending on the user change tracking.

It's possible to want all 0 defaults so not set it, but at the same time
still do some programmatic setting of configs with
evsel__set_config_if_unset(). Also if a PMU reverts to 0 defaults and
deletes its existing callback, it will silently break existing uses of
evsel__set_config_if_unset().

One way to fix this would be to assert in evsel__set_config_if_unset()
if the changes weren't tracked, but that would be a possibly untested
runtime failure. Instead, always track it as it's harmless and
simplifies testing too.

Signed-off-by: James Clark <james.clark@...aro.org>
---
 tools/perf/util/parse-events.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 7a3a90377896..c58829004fb4 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1528,12 +1528,8 @@ static int parse_events_add_pmu(struct parse_events_state *parse_state,
 		return -ENOMEM;
 	}
 
-	/*
-	 * When using default config, record which bits of attr->config were
-	 * changed by the user.
-	 */
-	if (pmu->perf_event_attr_init_default &&
-	    get_config_chgs(pmu, &parsed_terms, &config_terms)) {
+	/* Record which bits of attr->config were changed by the user. */
+	if (get_config_chgs(pmu, &parsed_terms, &config_terms)) {
 		parse_events_terms__exit(&parsed_terms);
 		return -ENOMEM;
 	}

-- 
2.34.1