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From: Jiri Olsa <jolsa@redhat.com>
To: Stephane Eranian <eranian@google.com>
Cc: Andi Kleen <andi@firstfloor.org>, Jiri Olsa <jolsa@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	David Ahern <dsahern@gmail.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Milian Wolff <milian.wolff@kdab.com>,
	frederic@kernel.org
Subject: Re: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event
Date: Fri, 8 Jun 2018 02:12:03 +0200	[thread overview]
Message-ID: <20180608001203.GB12322@krava> (raw)
In-Reply-To: <CABPqkBR88VBZB1mLttUx0UxnFgWTJ=ggb66PsMti--svJU70UQ@mail.gmail.com>

On Thu, Jun 07, 2018 at 09:01:30AM -0700, Stephane Eranian wrote:
> Hi Jiri,
> 
> On Thu, Jun 7, 2018 at 8:45 AM Andi Kleen <andi@firstfloor.org> wrote:
> >
> > On Thu, Jun 07, 2018 at 12:15:12AM +0200, Jiri Olsa wrote:
> > > Disable stopping of the idle tick when having live cputime
> > > event. When the tick is disabled, the idle counts are out
> > > of date until next tick/update and perf cputime PMU provides
> > > misleading counts.
> >
> > I really don't like this. This can totally change performance
> > (e.g. less Turbo due to less idle) and performance tools shouldn't
> > change the performance profile drastically.
> >
> You do not want to change the behavior of the kernel just because you
> are monitoring.
> This may introduce side effects on other events which may not otherwise exist.

right.. I guess we can survive few seconds of misleading idle counts
and perhaps we could detect nohz is enabled and warn about this

thanks,
jirka

  reply	other threads:[~2018-06-08  0:12 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-06 22:15 [RFC 00/10] perf: Add cputime events/metrics Jiri Olsa
2018-06-06 22:15 ` [PATCH 01/10] perf tools: Uniquify the event name if there's no other matched event Jiri Olsa
2018-06-06 23:19   ` Andi Kleen
2018-06-07  6:22     ` Jiri Olsa
2018-06-07 16:09       ` Stephane Eranian
2018-06-08  0:06         ` Jiri Olsa
2018-06-06 22:15 ` [PATCH 02/10] perf tools: Fix error index for pmu event parser Jiri Olsa
2018-06-07 18:53   ` Arnaldo Carvalho de Melo
2018-06-14  6:21   ` [tip:perf/urgent] " tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 03/10] perf stat: Add --interval-clear option Jiri Olsa
2018-06-07 18:57   ` Arnaldo Carvalho de Melo
2018-06-14  6:21   ` [tip:perf/urgent] " tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 04/10] perf stat: Use only color_fprintf call in print_metric_only Jiri Olsa
2018-06-07 19:00   ` Arnaldo Carvalho de Melo
2018-06-14  6:22   ` [tip:perf/urgent] " tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 05/10] perf stat: Fix metric column display Jiri Olsa
2018-06-07 19:00   ` Arnaldo Carvalho de Melo
2018-06-14  6:22   ` [tip:perf/urgent] perf stat: Fix metric column header display alignment tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 06/10] perf stat: Allow to specify specific metric column len Jiri Olsa
2018-06-14  6:23   ` [tip:perf/urgent] " tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 07/10] perf stat: Add event parsing error handling to add_default_attributes Jiri Olsa
2018-06-07 19:04   ` Arnaldo Carvalho de Melo
2018-06-07 19:05     ` Arnaldo Carvalho de Melo
2018-06-14  6:23   ` [tip:perf/urgent] " tip-bot for Jiri Olsa
2018-06-06 22:15 ` [PATCH 08/10] perf/cputime: Add cputime pmu Jiri Olsa
2018-06-06 22:15 ` [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event Jiri Olsa
2018-06-07 15:45   ` Andi Kleen
2018-06-07 16:01     ` Stephane Eranian
2018-06-08  0:12       ` Jiri Olsa [this message]
2018-06-06 22:15 ` [PATCH 10/10] perf stat: Add cputime metric support Jiri Olsa
2018-06-06 23:10 ` [RFC 00/10] perf: Add cputime events/metrics Andi Kleen
2018-09-26 14:44   ` Milian Wolff
2018-09-26 21:48     ` Jiri Olsa

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