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Subject: Re: [RFC][PATCH 0/6] perf: x86 RDPMC and RDTSC support
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Vince Weaver <vince@deater.net>
Cc: Vince Weaver <vweaver1@eecs.utk.edu>, mingo@elte.hu,
        William Cohen <wcohen@redhat.com>,
        Stephane Eranian <eranian@google.com>, Arun Sharma <asharma@fb.com>,
        linux-kernel@vger.kernel.org
Date: Wed, 21 Dec 2011 22:41:07 +0100
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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.