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

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Message-ID: <w2u850c51c31005031353x9be8ca7h90c244d64675ce3e@mail.gmail.com>
Date:	Mon, 3 May 2010 13:53:19 -0700
From:	Arun Sharma <aruns@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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 Mon, May 3, 2010 at 1:42 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, 2010-05-03 at 13:38 -0700, Arun Sharma wrote:
> > Enable PERF_SAMPLE_CPU by default. Implement --sort cpu.
>
> Why? The downside is that you unconditionally grow each sample and thus
> increase the overhead for something that doesn't make sense for the
> normal (task-inherit) case.

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 that's just our use case. The patch is mostly about --sort cpu
option. If you want to drop the part that enables PERF_SAMPLE_CPU by
default, that's fine by me.

 -Arun
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