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Date: Tue, 10 Apr 2012 22:47:12 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
        Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault
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On Tue, Apr 10, 2012 at 01:04:13PM +0300, Avi Kivity wrote:
> On 04/09/2012 10:46 PM, Marcelo Tosatti wrote:
> > Perhaps the mmu_lock hold times by get_dirty are a large component here?
> 
> That's my concern, because it affects the scaling of migration for wider
> guests.
> 
> > If that can be alleviated, not only RO->RW faults benefit.
> 
> Those are the most common types of faults on modern hardware, no?

Depends on your workload, of course. If there is memory pressure,
0->PRESENT might be very frequent. My point is that reduction of
mmu_lock contention is a good thing overall.