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

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Message-Id: <20081208.040204.139217002.davem@davemloft.net>
Date:	Mon, 08 Dec 2008 04:02:04 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mingo@...e.hu
Cc:	paulus@...ba.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	linux-arch@...r.kernel.org, akpm@...ux-foundation.org,
	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] Performance Counters for Linux, v2

From: Ingo Molnar <mingo@...e.hu>
Date: Mon, 8 Dec 2008 12:33:18 +0100

> Your whole statistical argument that group readout is a must-have for 
> precision is fundamentally flawed as well: counters _themselves_, as used 
> by most applications, by their nature, are a statistical sample to begin 
> with. There's way too many hardware events to track each of them 
> unintrusively - so this type of instrumentation is _all_ sampling based, 
> and fundamentally so. (with a few narrow exceptions such as single-event 
> interrupts for certain rare event types)

There are a lot of people who are going to fundamentally
disagree with this, myself included.

A lot of things are being stated about what people do with this stuff,
but I think there are people working longer in this area who quite
possibly know a lot better.  But they were blindsided by this new work
instead of being consulted, which was pretty unnice.
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