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>
---
tools/perf/Documentation/perf-stat.txt | 4 ++++
tools/perf/builtin-stat.c | 6 ++++++
tools/perf/util/evlist.c | 2 +-
tools/perf/util/evlist.h | 1 +
4 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index 1a766d4a2233..1ffb510606af 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -382,6 +382,10 @@ 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 affinities when iterating over CPUs. Disables
+an optimization aimed at minimizing interprocessor interrupts.
+
STAT RECORD
-----------
Stores stat data into perf data file.
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 75ff08c5f0ed..f2f149f0c2cf 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -2479,6 +2479,7 @@ 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 no_affinity = false;
struct option stat_options[] = {
OPT_BOOLEAN('T', "transaction", &transaction_run,
"hardware transaction statistics"),
@@ -2607,6 +2608,8 @@ 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(0, "no-affinity", &no_affinity,
+ "don't allow affinity optimizations aimed at reducing 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)",
@@ -2664,6 +2667,9 @@ int cmd_stat(int argc, const char **argv)
} else
stat_config.csv_sep = DEFAULT_SEPARATOR;
+ if (no_affinity)
+ evsel_list->no_affinity = true;
+
if (argc && strlen(argv[0]) > 2 && strstarts("record", argv[0])) {
argc = __cmd_record(stat_options, &opt_mode, argc, argv);
if (argc < 0)
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index fc3dae7cdfca..53c8e974de8b 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -368,7 +368,7 @@ static bool evlist__use_affinity(struct evlist *evlist)
struct perf_cpu_map *used_cpus = NULL;
bool ret = false;
- 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;
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index b4604c3f03d6..c7ba0e0b2219 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -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;
--
2.51.2.1041.gc1ab5b90ca-goog