linux-kernel - Re: [patch] Performance Counters for Linux, v3

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Date:	Fri, 12 Dec 2008 19:01:20 +0100
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Vince Weaver" <vince@...ter.net>, "Ingo Molnar" <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Eric Dumazet" <dada1@...mosbay.com>,
	"Robert Richter" <robert.richter@....com>,
	"Arjan van de Veen" <arjan@...radead.org>,
	"Peter Anvin" <hpa@...or.com>, "Paul Mackerras" <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [patch] Performance Counters for Linux, v3

Hi,

Given the level of abstractions you are using for the API, and given
your argument
that the kernel can do the HW resource scheduling better than anybody else.

What happens in the following test case:

   - 2-way system (cpu0, cpu1)

   - on cpu0, two processes P1, P2, each self-monitoring and counting event E1.
     Event E1 can only be measured on counter C1.

   - on cpu1, there is a cpu-wide session, monitoring event E1, thus using C1

   - the scheduler decides to migrate P1 onto CPU1. You now have a
conflict on C1.

How is this managed?
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