linux-kernel - [PATCH v4 04/14] perf evsel: Support sparse fields in evsel__set_config_if

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Message-Id: <20251222-james-perf-config-bits-v4-4-0608438186fc@linaro.org>
Date: Mon, 22 Dec 2025 15:14:29 +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>
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 v4 04/14] perf evsel: Support sparse fields in
 evsel__set_config_if_unset()

Sparse config fields are technically supported although currently
unused. field_prep() only works for contiguous bitfields so replace it
with pmu_format_value().

Reviewed-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: James Clark <james.clark@...aro.org>
---
 tools/perf/util/evsel.c | 4 +---
 tools/perf/util/pmu.c   | 3 +--
 tools/perf/util/pmu.h   | 1 +
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 21878e9bd029..45ab97beeb34 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1322,7 +1322,6 @@ struct evsel_config_term *__evsel__get_config_term(struct evsel *evsel, enum evs
  * the bit pattern. It is shifted into position by this function, so to set
  * something to true, pass 1 for val rather than a pre shifted value.
  */
-#define field_prep(_mask, _val) (((_val) << (ffsll(_mask) - 1)) & (_mask))
 void evsel__set_config_if_unset(struct evsel *evsel, const char *config_name,
 				u64 val)
 {
@@ -1339,8 +1338,7 @@ void evsel__set_config_if_unset(struct evsel *evsel, const char *config_name,
 		return;
 
 	/* Otherwise replace it */
-	evsel->core.attr.config &= ~bits;
-	evsel->core.attr.config |= field_prep(bits, val);
+	pmu_format_value(&bits, val, &evsel->core.attr.config, /*zero=*/true);
 }
 
 void __weak arch_evsel__set_sample_weight(struct evsel *evsel)
diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index e3a1f26213ec..599fdf5e28ba 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -1404,8 +1404,7 @@ int perf_pmu__format_type(struct perf_pmu *pmu, const char *name)
  * Sets value based on the format definition (format parameter)
  * and unformatted value (value parameter).
  */
-static void pmu_format_value(unsigned long *format, __u64 value, __u64 *v,
-			     bool zero)
+void pmu_format_value(unsigned long *format, __u64 value, __u64 *v, bool zero)
 {
 	unsigned long fbit, vbit;
 
diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index 8f11bfe8ed6d..e34db47ae5ef 100644
--- a/tools/perf/util/pmu.h
+++ b/tools/perf/util/pmu.h
@@ -254,6 +254,7 @@ int perf_pmu__check_alias(struct perf_pmu *pmu, struct parse_events_terms *head_
 			  u64 *alternate_hw_config, struct parse_events_error *err);
 int perf_pmu__find_event(struct perf_pmu *pmu, const char *event, void *state, pmu_event_callback cb);
 
+void pmu_format_value(unsigned long *format, __u64 value, __u64 *v, bool zero);
 void perf_pmu_format__set_value(void *format, int config, unsigned long *bits);
 bool perf_pmu__has_format(const struct perf_pmu *pmu, const char *name);
 int perf_pmu__for_each_format(struct perf_pmu *pmu, void *state, pmu_format_callback cb);

-- 
2.34.1