linux-kernel - Re: perf, H/W counters

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Message-ID: <20110527225145.GB847@dev1756.snc6.facebook.com>
Date:	Fri, 27 May 2011 15:51:45 -0700
From:	Arun Sharma <asharma@...com>
To:	David Ahern <dsahern@...il.com>
Cc:	"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf, H/W counters - ESX hosted VM

On Fri, May 27, 2011 at 01:33:54PM -0600, David Ahern wrote:
> 
> Has anyone successfully used perf within an ESX VM? dmesg shows a PMU is
> discovered:

Don't know about ESX. But in general, getting this right requires 
virtualizing PMU hardware (eg: save/restore PMU state on exit/entry
from the guest just the way the scheduler does for processes).

Also, the MSR read/writes to event-{select,count} registers must
be properly virtualized. Interrupt delivery (NMIs) is important
as well.

I suspect that MSR writes from the guest to the PMU related registers
are simply ignored in most virtual environments today.

 -Arun
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