Date: Wed, 14 Nov 2007 11:48:19 -0800 (PST)
Message-Id: <20071114.114819.97786038.davem@davemloft.net>
To: andi@firstfloor.org
Cc: hch@infradead.org, paulus@samba.org, akpm@linux-foundation.org,
       gregkh@suse.de, mucci@cs.utk.edu, eranian@hpl.hp.com, wcohen@redhat.com,
       robert.richter@amd.com, linux-kernel@vger.kernel.org,
       perfmon@napali.hpl.hp.com, perfmon2-devel@lists.sourceforge.net,
       ospat-devel@cs.utk.edu, ptools-perfapi@cs.utk.edu
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news
From: David Miller <davem@davemloft.net>
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From: Andi Kleen <andi@firstfloor.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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