linux-kernel - Re: [PATCH v1] perf stat: enable 1ms interval for printing event counters values

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Date:   Tue, 3 Apr 2018 17:22:04 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] perf stat: enable 1ms interval for printing event
 counters values

On Tue, Apr 03, 2018 at 06:04:13PM +0300, Alexey Budankov wrote:
> 
> Currently print count interval for performance counters values is 
> limited by 10ms so reading the values at frequencies higher than 100Hz 
> is restricted by the tool.
> 
> This change makes perf stat -I possible on frequencies up to 1KHz and, 
> to some extent, makes perf stat -I to be on-par with perf record 
> sampling profiling.
> 
> When running perf stat -I for monitoring e.g. PCIe uncore counters and 
> at the same time profiling some I/O workload by perf record e.g. for 
> cpu-cycles and context switches, it is then possible to observe 
> consolidated CPU/OS/IO(Uncore) performance picture for that workload.
> 
> Tool overhead warning printed when specifying -v option can be missed 
> due to screen scrolling in case you have output to the console 
> so message is moved into help available by running perf stat -h.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  tools/perf/builtin-stat.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)

I don't mind taking out the limit, but please update also
the stat man page, it mentiones the 10ms minimum

thanks,
jirka

> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index f5c454855908..147a27e8c937 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -1943,7 +1943,8 @@ static const struct option stat_options[] = {
>  	OPT_STRING(0, "post", &post_cmd, "command",
>  			"command to run after to the measured command"),
>  	OPT_UINTEGER('I', "interval-print", &stat_config.interval,
> -		    "print counts at regular interval in ms (>= 10)"),
> +		    "print counts at regular interval in ms "
> +		    "(overhead is possible for values <= 100ms)"),
>  	OPT_INTEGER(0, "interval-count", &stat_config.times,
>  		    "print counts for fixed number of times"),
>  	OPT_UINTEGER(0, "timeout", &stat_config.timeout,
> @@ -2923,17 +2924,6 @@ int cmd_stat(int argc, const char **argv)
>  		}
>  	}
>  
> -	if (interval && interval < 100) {
> -		if (interval < 10) {
> -			pr_err("print interval must be >= 10ms\n");
> -			parse_options_usage(stat_usage, stat_options, "I", 1);
> -			goto out;
> -		} else
> -			pr_warning("print interval < 100ms. "
> -				   "The overhead percentage could be high in some cases. "
> -				   "Please proceed with caution.\n");
> -	}
> -
>  	if (stat_config.times && interval)
>  		interval_count = true;
>  	else if (stat_config.times && !interval) {