linux-kernel - Re: [patch 2/3] performance counters: documentation

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Message-Id: <20081204.163741.48585912.davem@davemloft.net>
Date:	Thu, 04 Dec 2008 16:37:41 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	paulus@...ba.org
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org,
	mingo@...e.hu, eranian@...glemail.com, dada1@...mosbay.com,
	robert.richter@....com, arjan@...radead.org, hpa@...or.com,
	a.p.zijlstra@...llo.nl, rostedt@...dmis.org
Subject: Re: [patch 2/3] performance counters: documentation

From: Paul Mackerras <paulus@...ba.org>
Date: Fri, 5 Dec 2008 11:33:31 +1100

> This is going to be a huge problem, at least on powerpc, because it
> means that the kernel will have to know which events can be counted on
> which counters and what values need to be put in the control registers
> to select them.

Sparc64 is the same.

> The situation will be even worse with POWER5 and POWER6, where the
> event selection logic is very complex, with multiple layers of
> multiplexers.  I really really don't want the kernel to have to know
> about all that.

Niagara2 has deep multiplexing and sub-event masking too.

I really appreciated how perfmon kept all of those details
in userspace.
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