linux-kernel - Re: perf: is PERF_COUNT_SW_CONTEXT_SWITCHES a kernel or user event?

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Message-ID: <alpine.DEB.2.00.1106281326190.7766@cl320.eecs.utk.edu>
Date:	Tue, 28 Jun 2011 13:30:57 -0400 (EDT)
From:	Vince Weaver <vweaver1@...s.utk.edu>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...il.com>
Subject: Re: perf: is PERF_COUNT_SW_CONTEXT_SWITCHES a kernel or user
 event?

On Mon, 27 Jun 2011, Frederic Weisbecker wrote:
> 
> If you consider the strict meaning of exclude_user/exclude_kernel, they exclude
> events that _happen_ in user/kernel space. And context switches happen in kernel
> space.

I can see that it's somewhat arbitrary how context switches are 
classified.

I just want some assurances that now that it's moved to being
a kernel event it stays that way.

As it is, people upgrading from 2.6.32 to 2.6.34 and using the "cs:u"
event will suddently start getting "0" results.  

Possibly perf_events should just ignore exclude_kernel/exclude_user on an 
event like this where there is no real distinction.

Vince
vweaver1@...s.utk.edu
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