linux-kernel - Re: [PATCH v5 0/9] KVM: fast page fault

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Message-ID: <4FBDD5CA.9020906@linux.vnet.ibm.com>
Date:	Thu, 24 May 2012 14:31:38 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 0/9] KVM: fast page fault

On 05/23/2012 07:37 PM, Avi Kivity wrote:

> On 05/23/2012 11:51 AM, Xiao Guangrong wrote:
>> Changlog:
>> This are some changes from Marcelo's review:
>> - drop SPTE_WRITE_PROTECT bit, now, only one bit is needed to do
>>   lockless update.
>>
>> - always atomicly update spte if it can be updated out of mmu-lock.
>>
>> - flod the judgement of tlb flush into mmu_spte_update(), make the
>>   code easilyer audited.
>>
>> Performance result:
>> - autoest migration test (smp2.Fedora.16.64.migrate.with_autotest.dbench.unix):
>>                                                    before     after
>> smp2.Fedora.16.64.migrate.unix                        93      91    +2.1%
>> smp2.Fedora.16.64.migrate.with_autotest.dbench.unix   218     188   +13.7%
>>
>> - the benchmark attached is used to measure the resuming time
>>   after dirty-log
>>                             before            after
>> Run 10 times, Avg time:   512466818 ns.      269231261 ns   +47.5%
> 
> Still scary (esp. indirect sptes), but looks pretty good.


Hmm, i do not have a better way to solve the ABA problem on indirect spte now. :(
How about only allow fast page fault to work for direct spte?

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