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

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Message-ID: <AANLkTilvtBMOE6MecY4P51MLRz0-LRgru4lDBQrQnXbZ@mail.gmail.com>
Date:	Tue, 11 May 2010 17:17:11 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arnaldo Carvalho de Melo <acme@...radead.org>,
	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, May 11, 2010 at 5:13 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 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.
>

If inherit is the preferred default, then yes, the solution is to revert
the meaning of -i. You'd have to be consistent across all commands
using -i for inherit such as perf stat.
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