linux-kernel - Re: [patch] Performance Counters for Linux, v2

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Message-ID: <20081209112225.GD21618@elte.hu>
Date:	Tue, 9 Dec 2008 12:22:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	eranian@...il.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-arch@...r.kernel.org,
	akpm@...ux-foundation.org, dada1@...mosbay.com,
	robert.richter@....com, arjan@...radead.org, hpa@...or.com,
	a.p.zijlstra@...llo.nl, rostedt@...dmis.org, paulus@...ba.org
Subject: Re: [patch] Performance Counters for Linux, v2


* David Miller <davem@...emloft.net> wrote:

> From: Ingo Molnar <mingo@...e.hu>
> Date: Tue, 9 Dec 2008 12:02:46 +0100
> 
> > 
> > * stephane eranian <eranian@...glemail.com> wrote:
> > 
> > > > There's also more generic x86 support: all 4 generic PMCs of Nehalem 
> > > > / Core i7 are supported - i've run 4 instances of KernelTop and they 
> > > > used up four separate PMCs.
> > >
> > > Core/Atom have 5 counters, Nehalem has 7. Why are you not using all of 
> > > them already?
> > 
> > no, Nehalem has 4 generic purpose PMCs and 3 fixed-purpose PMCs (7 
> > total),
>  ...
> > Saying that it has 7 is misleading.
> 
> Even you just did.

which portion of my point stressing the general purpose attribute was 
unclear to you?

Saying it has 7 is misleading in the same way as if i told you now: 
"look, i have four eyes!". (they are: left eye looking right, left eye 
looking left, right eye looking left and right eye looking right)

Nehalem has 4 general purpose PMCs, not 7. Yes, it has 7 counters but 
they are not all general purpose. The P4 has 18.

	Ingo
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