Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample_period for libpfm4 events
From: Arnaldo Carvalho de Melo <acme@kernel.org>
Date: 2020-07-29 18:54:44
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Em Tue, Jul 28, 2020 at 01:57:31AM -0700, Ian Rogers escreveu:
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.
I tried the equivalent without libpfm and it works:
$ perf record -c 10000 -e cycles/period=20000/ sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.024 MB perf.data (23 samples) ]
$ perf evlist -v
cycles/period=20000/u: size: 120, { sample_period, sample_freq }: 20000, sample_type: IP|TID|TIME, read_format: ID, disabled: 1, inherit: 1, exclude_kernel: 1, exclude_hv: 1, mmap: 1, comm: 1, enable_on_exec: 1, task: 1, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
$
This was due to an ordering issue between libpfm4 parsing the event string and perf record initializing the event.
quoted hunk ↗ jump to hunk
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) { if (opts->freq) { attr->freq = 1; attr->sample_freq = opts->freq;-- 2.28.0.163.g6104cc2f0b6-goog
-- - Arnaldo