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

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Date:	Fri, 2 Oct 2015 20:50:15 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
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



> -----Original Message-----
> From: Arnaldo Carvalho de Melo [mailto:acme@...nel.org]
> Sent: Friday, October 02, 2015 4:40 PM
> To: Liang, Kan
> Cc: Jiri Olsa; jolsa@...nel.org; namhyung@...nel.org; ak@...ux.intel.com;
> linux-kernel@...r.kernel.org; Stephane Eranian
> 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?

Yes.

Thanks,
Kan

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