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

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Message-ID: <1324506779.17070.23.camel@twins>
Date:	Wed, 21 Dec 2011 23:32:59 +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 17:19 -0500, Vince Weaver wrote:
> 
> Speaking of bit 48, does your implementation do anything useful about
> the 32/40/48 bit limitation that some processors have with rdpmc?
> Or is the answer that if you might get overflow, then you have to use slow 
> syscall-based read? 

Yeah, we program an overflow interrupt around there (47 bits iirc) and
consume the total into the u64 count value and update the mmap control
page's offset.


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