linux-kernel - Re: [PATCH 1/1] perf,stat: reduce interval-print to 10ms

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Message-ID: <20151002204026.GC20515@kernel.org>
Date:	Fri, 2 Oct 2015 17:40:26 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/1] perf,stat: reduce interval-print to 10ms

Em Fri, Oct 02, 2015 at 08:22:06PM +0000, Liang, Kan escreveu:
> > > > +		if (interval < 10) {
> > > > +			pr_err("print interval must be >= 10ms\n");
> > > > +			parse_options_usage(stat_usage, 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");
> > >
> > > with '-I' 10 this warning flies away quite fast ;-)
> > >
> > > I guess it's better than nothing, and I'm not sure about putting some
> > > sleep after that warning..
> > >
> > > Acked-by: Jiri Olsa <jolsa@...nel.org>
> > 
> > Right, this should appear in the man page as well, I added the patch below,
> > we could also print that warning when the workload ends.
 
> OK. We can print the warning message again at the end as the patch below.
> 
> +++ b/tools/perf/builtin-stat.c
> @@ -1377,6 +1377,11 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused)
>  	if (!forever && status != -1 && !interval)
>  		print_counters(NULL, argc, argv);
>  
> +	if (interval && interval < 100)
> +		pr_warning("print interval < 100ms. "
> +			   "The overhead percentage could be high in some cases. "
> +			   "Please proceed with caution.\n");

Yeah, something like that, but the warning then becomes strange,
"proceed"? I guess that something like:

		pr_warning("print interval < 100ms. "
			   "The overhead percentage could have been high. "
			   "Take that into account when interpreting the these numbers.\n");

Right?

- Arnaldo

> +
>  	perf_evlist__free_stats(evsel_list);
>  out:
>  	perf_evlist__delete(evsel_list);
--
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