linux-kernel - Re: [PATCH] perf: implement recording/reporting per-cpu samples

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Message-ID: <AANLkTim4UdMxxPkhHjVd_433Uk2QoVXBTy44KUlRBNSX@mail.gmail.com>
Date:	Thu, 27 May 2010 13:54:46 -0700
From:	Arun Sharma <aruns@...gle.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com
Subject: Re: [PATCH] perf: implement recording/reporting per-cpu samples

On Thu, May 27, 2010 at 11:41 AM, Arnaldo Carvalho de Melo
<acme@...stprotocols.net> wrote:
> Em Wed, May 05, 2010 at 11:16:12AM -0700, Arun Sharma escreveu:
>> On Tue, May 04, 2010 at 11:16:38AM +0200, Peter Zijlstra wrote:
>> > > In a shared multi-core environment, users want to analyze why their
>> > > program was slow. In particular, if the code ran slower only on
>> > > certain CPUs due to interference from other programs or kernel
>> > > threads, they want to know that.
>> >
>> > But for that you use perf record -a, right? So you record all cpus
>> > allways -- otherwise there is no telling what was happening to make it
>> > go slow.
>>
>> The updated patch records the CPU only in the system_wide mode.
>
> I think this should be done only if you'll actually need it, as in,
> "cpu" is one of the sort keys, but that can be done as a followup patch,
> but there is another thing I think you need to change, see below.
>

How would you know if the user is going to sort by cpu at "perf record" time?

Thanks for taking care of the second part.

 -Arun
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