linux-kernel - Re: [RFC][PATCH 0/6] perf: x86 RDPMC and RDTSC support

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Message-ID: <1324503667.17070.7.camel@twins>
Date:	Wed, 21 Dec 2011 22:41:07 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vince Weaver <vince@...ter.net>
Cc:	Vince Weaver <vweaver1@...s.utk.edu>, mingo@...e.hu,
	William Cohen <wcohen@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Arun Sharma <asharma@...com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 0/6] perf: x86 RDPMC and RDTSC support

On Wed, 2011-12-21 at 16:32 -0500, Vince Weaver wrote:

> * One, is it possible to detect at runtime that rdpmc() is supported?  
>   Maybe a field in the mmap'd buffer that can be read?

Ingo suggested a similar thing, will implement (although Christmas might
interfere with delivery timelines etc..).

> * Second, if I try a start / run 100M instructions / read
>   and measure retired instructions I get:
>       281474977711543 instructions
>   This is 0x10000000f45b7 which is 1<<48 + 100M.  I guess an artifact
>   of how the counters are set up?  Is it possible to have this start
>   at 0?  

Its supposed to be 0 based, clearly I messed up something and need to go
figure out what. Thanks for reporting.
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