linux-kernel - Re: [RFC/PATCH 10/10] perf tools: Change default calchain percent limit to 0.005%

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Message-ID: <20160127160611.GI31686@two.firstfloor.org>
Date:	Wed, 27 Jan 2016 17:06:12 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Wang Nan <wangnan0@...wei.com>,
	Taeung Song <treeze.taeung@...il.com>
Subject: Re: [RFC/PATCH 10/10] perf tools: Change default calchain percent
 limit to 0.005%

On Thu, Jan 28, 2016 at 12:40:57AM +0900, Namhyung Kim wrote:
> The current default limit of 0.5% is (mostly) for 'fractal' mode which
> calculates the percentage relatively.  As we changed the default
> callchain mode to 'graph', the existing limit is too high IMHO.
> Normally there're many entries under 0.5% overhead, it'd be supprising
> that they don't show callchains.

It's too small imho. On more complex workloads with a lot of user space
code we often end up with default perf report --stdio callgraph output of several
hundred KB, and most of it is useless as it is only very small.

-Andi