linux-kernel - Re: [perfmon] Re: [perfmon2] perfmon2 merge news

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Message-Id: <20071114.114819.97786038.davem@davemloft.net>
Date:	Wed, 14 Nov 2007 11:48:19 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	andi@...stfloor.org
Cc:	hch@...radead.org, paulus@...ba.org, akpm@...ux-foundation.org,
	gregkh@...e.de, mucci@...utk.edu, eranian@....hp.com,
	wcohen@...hat.com, robert.richter@....com,
	linux-kernel@...r.kernel.org, perfmon@...ali.hpl.hp.com,
	perfmon2-devel@...ts.sourceforge.net, ospat-devel@...utk.edu,
	ptools-perfapi@...utk.edu
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news

From: Andi Kleen <andi@...stfloor.org>
Date: Wed, 14 Nov 2007 13:38:38 +0100

> At least for x86 and I suspect some 1other architectures we don't
> initially need a syscall at all for this. There is an instruction
> RDPMC who can read a performance counter just fine. It is also much
> faster and generally preferable for the case where a process measures
> events about itself. In fact it is essential for one of the use cases
> I would like to see perfmon used (replacement of RDTSC for cycle
> counting) 

I wouldn't even want to use a syscall for something like
that on Sparc, I'd rather give this a dedicated software
trap so that I can code it completely in assembler.
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