linux-kernel - Re: [PATCH 4/8] KVM: avoid unnecessary wait for a async pf

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Message-ID: <4CC920F2.4080008@cn.fujitsu.com>
Date:	Thu, 28 Oct 2010 15:06:26 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 4/8] KVM: avoid unnecessary wait for a async pf

On 10/27/2010 06:42 PM, Gleb Natapov wrote:
> On Wed, Oct 27, 2010 at 05:04:58PM +0800, Xiao Guangrong wrote:
>> In current code, it checks async pf completion out of the wait context,
>> like this:
>>
>> if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
>> 		    !vcpu->arch.apf.halted)
>> 			r = vcpu_enter_guest(vcpu);
>> 		else {
>> 			......
>> 			kvm_vcpu_block(vcpu)
>> 			 ^- waiting until 'async_pf.done' is not empty
>> }
>> 	
>> kvm_check_async_pf_completion(vcpu)
>>  ^- delete list from async_pf.done
>>
>> So, if we check aysnc pf completion first, it can be blocked at
>> kvm_vcpu_block
>>
> Correct, but it can be fixed by adding vcpu->arch.apf.halted = false; to
> kvm_arch_async_page_present(), no?
> Adding kvm_check_async_pf_completion() to arch independent kvm_vcpu_block()
> constrains how other archs may implement async pf support IMO.
>  

Um, i think it's reasonable, will fix it address your comment.
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