linux-kernel - Re: [RFC] perf: perf record sets inherit by default

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Date:	Tue, 11 May 2010 17:13:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	mingo@...e.hu, Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>,
	perfmon2-devel@...ts.sf.net
Subject: Re: [RFC] perf: perf record sets inherit by default

On Tue, 2010-05-11 at 12:00 -0300, Arnaldo Carvalho de Melo wrote:
> 
> Humm, since for -C and -a using -i doesn't make sense, I guess it should
> be off by default and only be auto-activated if we don't specify any
> option, i.e. when using it like:
> 
> perf record ./hackbench
> 
> What do you think? 

-ENOPARSE

-a/-C usage creates per-cpu counters and will thus ignore any and all
perf_event_attr::inherit state.

Your above suggestion would still have inherit enabled by default, and
would thus not change anything.

The thing is that perf-record defaults to inherited per-task-per-cpu
counters, which, I think, is a reasonable default, just sub-optimal for
single threaded/!forking subjects.

So what would make sense is for -i to mean --no-inherit, and for !
inherit create a per-task counter instead of a per-task-per-cpu counter.

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