linux-kernel - Re: [PATCH][KVM][retry 3] Add support for Pause Filtering to AMD SVM

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Date:	Wed, 20 May 2009 11:10:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Mark Langsdorf <mark.langsdorf@....com>,
	Joerg Roedel <joerg.roedel@....com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][KVM][retry 3] Add support for Pause Filtering to AMD
 SVM

On Wed, 2009-05-20 at 12:04 +0300, Avi Kivity wrote:
> Peter Zijlstra wrote:

> >> It's a fully virtualized guest.  There's no way to get this without 
> >> patching the guest kernel.
> >>     
> >
> > Yes there is.. virtualized monitor-wait stuff coupled with a
> > monitor-wait based spinlock implementation.
> >   
> 
> That only works if the guest uses monitor/mwait.  Not all of the guests 
> are under our control.  I don't know whether Windows uses 
> monitor/mwait.  Further, we don't have timed exits on mwait like we do 
> with pause.

Ugh, you really care about crap like windows?

> I've also heard that monitor/mwait are very slow and only usable on idle 
> loop stuff.

Yeah, current implementations suck, doesn't mean it has to stay that
way.

> > Once we go change silicon, you might as well do it right.
> >   
> 
> None of the major x86 vendors are under my control.

I thought this patch came from AMD, who changed their silicon so 'solve'
one of these virt problems.

/me goes hide again, and pretend all of virt doesn't exist :-) Think
happy thoughts.
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