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perf stat: Add no-affinity flag

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Add flag that disables affinity behavior.

Using sched_setaffinity() to place a perf thread on a CPU can avoid
certain interprocessor interrupts but may introduce a delay due to the
scheduling, particularly on loaded machines.

Add a command line option to disable the behavior.

This behavior is less present in other tools like `perf record`, as it
uses a ring buffer and doesn't make repeated system calls.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Falcon <thomas.falcon@intel.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Ian Rogers 2026-02-09 22:03:59 -08:00 • committed by Arnaldo Carvalho de Melo
parent d484361550
commit 5d1ab659fb
4 changed files with 13 additions and 5 deletions
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5
tools/perf/Documentation/perf-stat.txt
View file

@ -382,6 +382,11 @@ color the metric's computed value.
Don't print output, warnings or messages. This is useful with perf stat
record below to only write data to the perf.data file.
--no-affinity::
Don't change scheduler CPU affinities when iterating over
CPUs. Disables an optimization aimed at minimizing interprocessor
interrupts.
STAT RECORD
-----------
Stores stat data into perf data file.

6
tools/perf/builtin-stat.c
View file

@ -2426,6 +2426,7 @@ static int parse_tpebs_mode(const struct option *opt, const char *str,
int cmd_stat(int argc, const char **argv)
{
struct opt_aggr_mode opt_mode = {};
bool affinity = true, affinity_set = false;
struct option stat_options[] = {
OPT_BOOLEAN('T', "transaction", &transaction_run,
"hardware transaction statistics"),
@ -2554,6 +2555,8 @@ int cmd_stat(int argc, const char **argv)
"don't print 'summary' for CSV summary output"),
OPT_BOOLEAN(0, "quiet", &quiet,
"don't print any output, messages or warnings (useful with record)"),
OPT_BOOLEAN_SET(0, "affinity", &affinity, &affinity_set,
"enable (default) or disable affinity optimizations to reduce IPIs"),
OPT_CALLBACK(0, "cputype", &evsel_list, "hybrid cpu type",
"Only enable events on applying cpu with this type "
"for hybrid platform (e.g. core or atom)",
@ -2611,6 +2614,9 @@ int cmd_stat(int argc, const char **argv)
} else
stat_config.csv_sep = DEFAULT_SEPARATOR;
if (affinity_set)
evsel_list->no_affinity = !affinity;
if (argc && strlen(argv[0]) > 2 && strstarts("record", argv[0])) {
argc = __cmd_record(stat_options, &opt_mode, argc, argv);
if (argc < 0)

6
tools/perf/util/evlist.c
View file

@ -369,11 +369,7 @@ static bool evlist__use_affinity(struct evlist *evlist)
struct perf_cpu_map *used_cpus = NULL;
bool ret = false;
/*
* With perf record core.user_requested_cpus is usually NULL.
* Use the old method to handle this for now.
*/
if (!evlist->core.user_requested_cpus ||
if (evlist->no_affinity || !evlist->core.user_requested_cpus ||
cpu_map__is_dummy(evlist->core.user_requested_cpus))
return false;

1
tools/perf/util/evlist.h
View file

@ -59,6 +59,7 @@ struct event_enable_timer;
struct evlist {
struct perf_evlist core;
bool enabled;
bool no_affinity;
int id_pos;
int is_pos;
int nr_br_cntr;