Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample_period for libpfm4 events

On Tue, Jul 28, 2020 at 05:59:46PM +0200, Jiri Olsa wrote:

On Tue, Jul 28, 2020 at 01:57:31AM -0700, Ian Rogers wrote:

quoted

From: Stephane Eranian <redacted>

Before:
$ perf record -c 10000 --pfm-events=cycles:period=77777

Would yield a cycles event with period=10000, instead of 77777.

This was due to an ordering issue between libpfm4 parsing
the event string and perf record initializing the event.

This patch fixes the problem by preventing override for
events with attr->sample_period != 0 by the time
perf_evsel__config() is invoked. This seems to have been the
intent of the author.

Signed-off-by: Stephane Eranian <redacted>
Reviewed-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/evsel.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 811f538f7d77..8afc24e2ec52 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c

@@ -976,8 +976,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
 	 * We default some events to have a default interval. But keep
 	 * it a weak assumption overridable by the user.
 	 */
-	if (!attr->sample_period || (opts->user_freq != UINT_MAX ||
-				     opts->user_interval != ULLONG_MAX)) {
+	if (!attr->sample_period) {

I was wondering why this wouldn't break record/top
but we take care of the via record_opts__config

as long as 'perf test attr' works it looks ok to me

hum ;-)

[jolsa@krava perf]$ sudo ./perf test 17 -v
17: Setup struct perf_event_attr                          :
...
running './tests/attr/test-record-C0'
expected sample_period=4000, got 3000
FAILED './tests/attr/test-record-C0' - match failure

jirka

Acked-by: Jiri Olsa <redacted>

thanks,
jirka