linux-kernel - Re: [PATCH] perf record: Disallow -c and -F option at the same time

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Date:   Fri, 2 Apr 2021 10:37:02 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>
Subject: Re: [PATCH] perf record: Disallow -c and -F option at the same time

Em Fri, Apr 02, 2021 at 06:40:20PM +0900, Namhyung Kim escreveu:
> It's confusing which one is effective when the both options are given.
> The current code happens to use -c in this case but users might not be
> aware of it.  We can change it to complain about that instead of
> relying on the implicit priority.
> 
> Before:
>   $ perf record -c 111111 -F 99 true
>   [ perf record: Woken up 1 times to write data ]
>   [ perf record: Captured and wrote 0.031 MB perf.data (8 samples) ]
> 
>   $ perf evlist -F
>   cycles: sample_period=111111
> 
> After:
>   $ perf record -c 111111 -F 99 true
>   cannot set frequency and period at the same time
> 
> So this change can break existing usages, but I think it's rare to
> have both options and it'd be better changing them.

Humm, perhaps we can just make that an warning stating that -c is used
if both are specified?

$ perf record -c 111111 -F 99 true
Frequency and period can't be used the same time, -c 11111 will be used.

- Arnaldo
 
> Suggested-by: Alexey Alexandrov <aalexand@...gle.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/record.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
> index f99852d54b14..43e5b563dee8 100644
> --- a/tools/perf/util/record.c
> +++ b/tools/perf/util/record.c
> @@ -157,9 +157,15 @@ static int get_max_rate(unsigned int *rate)
>  static int record_opts__config_freq(struct record_opts *opts)
>  {
>  	bool user_freq = opts->user_freq != UINT_MAX;
> +	bool user_interval = opts->user_interval != ULLONG_MAX;
>  	unsigned int max_rate;
>  
> -	if (opts->user_interval != ULLONG_MAX)
> +	if (user_interval && user_freq) {
> +		pr_err("cannot set frequency and period at the same time\n");
> +		return -1;
> +	}
> +
> +	if (user_interval)
>  		opts->default_interval = opts->user_interval;
>  	if (user_freq)
>  		opts->freq = opts->user_freq;
> -- 
> 2.31.0.208.g409f899ff0-goog
> 

-- 

- Arnaldo