linux-kernel - Re: [PATCH 3/3] perf tools: Check maximum frequency rate for record/top

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Message-ID: <20131104153216.GC2805@krava.brq.redhat.com>
Date:	Mon, 4 Nov 2013 16:32:16 +0100
From:	Jiri Olsa <jolsa@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 3/3] perf tools: Check maximum frequency rate for
 record/top

On Mon, Nov 04, 2013 at 08:17:24AM -0700, David Ahern wrote:
> On 11/4/13, 4:06 AM, Jiri Olsa wrote:
> >Adding the check for maximum allowed frequency rate
> >defined in following file:
> >   /proc/sys/kernel/perf_event_max_sample_rate
> >
> >When we cross the maximum value we fail and display
> >detailed error message with advise.
> 
> perf commands should automatically adjust the default frequency too.
> If the user did not specify a frequency then this message is going
> to be confusing.

ok, I'll add that check and probably some warning
if we are force to go below the default rate.

> 
> Though the algorithm that keeps lowering the rate should be tweaked as well.

yea.. I was thinking putting the max rate back up after
some sane period

or/plus having 'echo 0 > /proc/sys/kernel/perf_event_max_sample_rate' to
disable it completely

jirka
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