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

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Date:	Wed, 20 May 2009 10:54:17 +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 11:49 +0300, Avi Kivity wrote:
> Peter Zijlstra wrote:
> >>> That said, I still thoroughly dislike this whole approach.
> >>>   
> >>>       
> >> Can you explain why?  We have a thread that has detected that it's 
> >> spinning.  Keeping on spinning is a waste of cpu time.  Why not let 
> >> something else use the cpu?
> >>     
> >
> > Because its a polling interface. I much prefer it if we were to get a
> > wakeup notification when the vcpu holding the lock releases it.
> >   
> 
> 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.

Once we go change silicon, you might as well do it right.
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