linux-kernel - Re: [PATCH] perf_event use rdpmc rather than rdmsr when possible in kernel

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Date:	Mon, 27 Feb 2012 12:04:27 -0500
From:	Vince Weaver <vweaver1@...s.utk.edu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	<linux-kernel@...r.kernel.org>, <mingo@...e.hu>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stephane Eranian <eranian@...il.com>
Subject: Re: [PATCH] perf_event use rdpmc rather than rdmsr when possible in
 kernel

On Mon, 27 Feb 2012, Peter Zijlstra wrote:

> > I couldn't find another usable rdpmc() call in the kernel.  Should I add 
> > one?  I admit I hadn't thought that this might break VMs not expecting
> > rdpmc calls from the kernel. 
> 
> arch/x86/include/asm/msr.h
> 
> #define rdpmc(counter, low, high)                       \                                    
> do {                                                    \                                    
>         u64 _l = native_read_pmc((counter));            \                                    
>         (low)  = (u32)_l;                               \                                    
>         (high) = (u32)(_l >> 32);                       \                                    
> } while (0)

ugh I did multiple recursive greps, and definitely searched msr.h by
hand various times looking for that and I somehow missed it each time.

I'll update the patch.

Vince

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