linux-kernel - Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch and pte prefetch

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Date:	Wed, 07 Jul 2010 22:10:04 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch
 and pte prefetch



Marcelo Tosatti wrote:

>>>>
>>>> It reads the 16 aligned items around sptep's corresponding gpte and this gpte
>>>> is also in this area. :-)
>>> But you removed that in patch 8?
>>>
>> Oh, i just want it good for review, you mean it's better let patch 7 and 8 in one patch?
> 
> I mean patch 7 is wrong because it removes rereading of gpte, with
> mmu_lock held, in the prefetch patch.
> 

Marcelo,

Sorry, i don't understand it clearly.

In the patch 7, we read gpte like this:

	hold mmu_lock
	atomic read gpte during guest mapping's checking in 'fetch' path
	atomic read 16 aligned items chunk (include gpte) in pte_prefetch path
	release mmu_lock

And in the patch 8, we do it like this:
	hold mmu_lock

	atomic read 16 aligned items chunk (include gpte) in 'fetch' path, and
        saved this chunk to gw->prefetch_ptes
	
        get gptes form gw->prefetch_ptes in pte_prefetch path

	release mmu_lock

Could you please tell me where is wrong?

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