linux-kernel - Re: [PATCH v2 2/5] perf record: Prevent override of attr->sample

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Message-ID: <20200728155940.GC1319041@krava>
Date:   Tue, 28 Jul 2020 17:59:40 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 2/5] perf record: Prevent override of
 attr->sample_period for libpfm4 events

On Tue, Jul 28, 2020 at 01:57:31AM -0700, Ian Rogers wrote:
> From: Stephane Eranian <eranian@...gle.com>
> 
> 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 <eranian@...gle.com>
> Reviewed-by: Ian Rogers <irogers@...gle.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

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka