linux-kernel - Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts

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Message-ID: <18966.31089.52074.614650@cargo.ozlabs.ibm.com>
Date:	Fri, 22 May 2009 20:07:45 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] perf_counter: optimize context switch between
 identical inherited contexts

Peter Zijlstra writes:

> Ah, should I read this as 'n' lmbench instances on a single cpu? So that
> we get multiple inheritance sets mixed and have to switch between them?

No, it's one lat_ctx instance, which creates N processes connected in
a ring with pipes, and passes a token around some number of times and
measures the overall time to do that.  It subtracts off the time it
takes to do all the pipe reads and writes in a single process to get
an estimate of how much the context switches are costing.

Paul.
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