netdev - Re: [PATCH v2] perf record/arm-spe: Override attr->sample

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Date:   Sat, 22 Jan 2022 17:15:29 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     German Gomez <german.gomez@....com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Chase Conklin <chase.conklin@....com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Stephane Eranian <eranian@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v2] perf record/arm-spe: Override attr->sample_period for
 non-libpfm4 events

Em Tue, Jan 18, 2022 at 02:40:54PM +0000, German Gomez escreveu:
> A previous patch preventing "attr->sample_period" values from being
> overridden in pfm events changed a related behaviour in arm-spe.
> 
> Before said patch:
> perf record -c 10000 -e arm_spe_0// -- sleep 1
> 
> Would yield an SPE event with period=10000. After the patch, the period
> in "-c 10000" was being ignored because the arm-spe code initializes
> sample_period to a non-zero value.
> 
> This patch restores the previous behaviour for non-libpfm4 events.
> 
> Reported-by: Chase Conklin <chase.conklin@....com>
> Fixes: ae5dcc8abe31 (“perf record: Prevent override of attr->sample_period for libpfm4 events”)
> Signed-off-by: German Gomez <german.gomez@....com>
> ---
> As suggested by Arnaldo, this v2 doesn't include a test in order to not
> block this fix for longer than necessary. So the test can be sent as a
> separate submission later.

Got it, will apply.
 
> Changes since v1.
>  - Update commit message (James Clark)
> ---
>  tools/perf/util/evsel.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index a59fb2ecb84e..86ab038f020f 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1065,6 +1065,17 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un
>  {
>  }
>  
> +static void evsel__set_default_freq_period(struct record_opts *opts,
> +					   struct perf_event_attr *attr)
> +{
> +	if (opts->freq) {
> +		attr->freq = 1;
> +		attr->sample_freq = opts->freq;
> +	} else {
> +		attr->sample_period = opts->default_interval;
> +	}
> +}
> +
>  /*
>   * The enable_on_exec/disabled value strategy:
>   *
> @@ -1131,14 +1142,12 @@ 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) {
> -		if (opts->freq) {
> -			attr->freq		= 1;
> -			attr->sample_freq	= opts->freq;
> -		} else {
> -			attr->sample_period = opts->default_interval;
> -		}
> -	}
> +	if ((evsel->is_libpfm_event && !attr->sample_period) ||
> +	    (!evsel->is_libpfm_event && (!attr->sample_period ||
> +					 opts->user_freq != UINT_MAX ||
> +					 opts->user_interval != ULLONG_MAX)))
> +		evsel__set_default_freq_period(opts, attr);
> +
>  	/*
>  	 * If attr->freq was set (here or earlier), ask for period
>  	 * to be sampled.
> -- 
> 2.25.1

-- 

- Arnaldo