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Date: Mon, 26 Oct 2020 23:19:37 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Andi Kleen <ak@...ux.intel.com>
Cc: Ingo Molnar <mingo@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
LKML <linux-kernel@...r.kernel.org>,
Stephane Eranian <eranian@...gle.com>,
Ian Rogers <irogers@...gle.com>
Subject: [RFC] perf evlist: Warn if event group has mixed sw/hw events
I found that order of events in a group impacts performance during the
open. If a group has a software event as a leader and has other
hardware events, the lead needs to be moved to a hardware context.
This includes RCU synchronization which takes about 20 msec on my
system. And this is just for a single group, so total time increases
in proportion to the number of event groups and the number of cpus.
On my 36 cpu system, opening 3 groups system-wide takes more than 2
seconds. You can see and compare it easily with the following:
$ time ./perf stat -a -e '{cs,cycles},{cs,cycles},{cs,cycles}' sleep 1
...
1.006333430 seconds time elapsed
real 0m3.969s
user 0m0.089s
sys 0m0.074s
$ time ./perf stat -a -e '{cycles,cs},{cycles,cs},{cycles,cs}' sleep 1
...
1.006755292 seconds time elapsed
real 0m1.144s
user 0m0.067s
sys 0m0.083s
This patch just added a warning before running it. I'd really want to
fix the kernel if possible but don't have a good idea. Thoughts?
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
tools/perf/builtin-record.c | 2 +
tools/perf/builtin-stat.c | 2 +
tools/perf/builtin-top.c | 2 +
tools/perf/util/evlist.c | 78 +++++++++++++++++++++++++++++++++++++
tools/perf/util/evlist.h | 1 +
5 files changed, 85 insertions(+)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index adf311d15d3d..c0b08cacbae0 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -912,6 +912,8 @@ static int record__open(struct record *rec)
perf_evlist__config(evlist, opts, &callchain_param);
+ evlist__warn_mixed_group(evlist);
+
evlist__for_each_entry(evlist, pos) {
try_again:
if (evsel__open(pos, pos->core.cpus, pos->core.threads) < 0) {
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index b01af171d94f..d5d4e02bda69 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -738,6 +738,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
if (affinity__setup(&affinity) < 0)
return -1;
+ evlist__warn_mixed_group(evsel_list);
+
evlist__for_each_cpu (evsel_list, i, cpu) {
affinity__set(&affinity, cpu);
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 7c64134472c7..9ad319cea948 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -1027,6 +1027,8 @@ static int perf_top__start_counters(struct perf_top *top)
perf_evlist__config(evlist, opts, &callchain_param);
+ evlist__warn_mixed_group(evlist);
+
evlist__for_each_entry(evlist, counter) {
try_again:
if (evsel__open(counter, top->evlist->core.cpus,
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 8bdf3d2c907c..02cff39e509e 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -28,6 +28,7 @@
#include <unistd.h>
#include <sched.h>
#include <stdlib.h>
+#include <dirent.h>
#include "parse-events.h"
#include <subcmd/parse-options.h>
@@ -1980,3 +1981,80 @@ struct evsel *evlist__find_evsel(struct evlist *evlist, int idx)
}
return NULL;
}
+
+static int *sw_types;
+static int nr_sw_types;
+
+static void collect_software_pmu_types(void)
+{
+ const char *known_sw_pmu[] = {
+ "software", "tracepoint", "breakpoint", "kprobe", "uprobe", "msr"
+ };
+ DIR *dir;
+ struct dirent *d;
+ char path[PATH_MAX];
+ int i;
+
+ if (sw_types != NULL)
+ return;
+
+ nr_sw_types = ARRAY_SIZE(known_sw_pmu);
+ sw_types = calloc(nr_sw_types, sizeof(int));
+ if (sw_types == NULL) {
+ pr_err("Memory allocation failed!\n");
+ return;
+ }
+
+ dir = opendir("/sys/bus/event_source/devices");
+ while ((d = readdir(dir)) != NULL) {
+ for (i = 0; i < nr_sw_types; i++) {
+ if (strcmp(d->d_name, known_sw_pmu[i]))
+ continue;
+
+ snprintf(path, sizeof(path), "%s/%s/type",
+ "bus/event_source/devices", d->d_name);
+ sysfs__read_int(path, &sw_types[i]);
+ }
+ }
+ closedir(dir);
+}
+
+static bool is_software_event(struct evsel *evsel)
+{
+ int i;
+
+ for (i = 0; i < nr_sw_types; i++) {
+ if (evsel->core.attr.type == (unsigned)sw_types[i])
+ return true;
+ }
+ return false;
+}
+
+void evlist__warn_mixed_group(struct evlist *evlist)
+{
+ struct evsel *leader, *evsel;
+ bool warn = true;
+
+ collect_software_pmu_types();
+
+ /* Warn if an event group has a sw leader and hw siblings */
+ evlist__for_each_entry(evlist, leader) {
+ if (!evsel__is_group_event(leader))
+ continue;
+
+ if (!is_software_event(leader))
+ continue;
+
+ for_each_group_member(evsel, leader) {
+ if (is_software_event(evsel))
+ continue;
+ if (!warn)
+ continue;
+
+ pr_warning("WARNING: Event group has mixed hw/sw events.\n"
+ "This will slow down the perf_event_open syscall.\n"
+ "Consider putting a hw event as a leader.\n\n");
+ warn = false;
+ }
+ }
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index e1a450322bc5..a5b0a1d03a00 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -387,4 +387,5 @@ int evlist__ctlfd_ack(struct evlist *evlist);
#define EVLIST_DISABLED_MSG "Events disabled\n"
struct evsel *evlist__find_evsel(struct evlist *evlist, int idx);
+void evlist__warn_mixed_group(struct evlist *evlist);
#endif /* __PERF_EVLIST_H */
--
2.29.0.rc1.297.gfa9743e501-goog
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