linux-kernel - Re: [PATCH v2 1/5] perf record: Set PERF_RECORD

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Date:   Wed, 29 Jul 2020 15:52:12 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.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>,
        David Sharp <dhsharp@...gle.com>
Subject: Re: [PATCH v2 1/5] perf record: Set PERF_RECORD_PERIOD if attr->freq
 is set.

Em Tue, Jul 28, 2020 at 01:57:30AM -0700, Ian Rogers escreveu:
> From: David Sharp <dhsharp@...gle.com>
> 
> evsel__config() would only set PERF_RECORD_PERIOD if it set attr->freq

There is no such thing as 'PERF_RECORD_PERIOD', its PERF_SAMPLE_PERIOD,
also...

> from perf record options. When it is set by libpfm events, it would not
> get set. This changes evsel__config to see if attr->freq is set outside of
> whether or not it changes attr->freq itself.
> 
> Signed-off-by: David Sharp <dhsharp@...gle.com>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/util/evsel.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index ef802f6d40c1..811f538f7d77 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -979,13 +979,18 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
>  	if (!attr->sample_period || (opts->user_freq != UINT_MAX ||
>  				     opts->user_interval != ULLONG_MAX)) {
>  		if (opts->freq) {
> -			evsel__set_sample_bit(evsel, PERIOD);
>  			attr->freq		= 1;
>  			attr->sample_freq	= opts->freq;
>  		} else {
>  			attr->sample_period = opts->default_interval;
>  		}
>  	}
> +	/*
> +	 * If attr->freq was set (here or earlier), ask for period
> +	 * to be sampled.
> +	 */
> +	if (attr->freq)
> +		evsel__set_sample_bit(evsel, PERIOD);

Why can't the libpfm code set opts?

With this patch we will end up calling evsel__set_sample_bit(evsel,
PERIOD) twice, which isn't a problem but looks strange.

- Arnaldo

>  
>  	if (opts->no_samples)
>  		attr->sample_freq = 0;
> -- 
> 2.28.0.163.g6104cc2f0b6-goog
> 

-- 

- Arnaldo