linux-kernel - Re: [PATCH 3/4] PF: Provide additional direct page notification

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Date:	Wed, 10 Jul 2013 12:52:06 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Dominik Dingel <dingel@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Xiantao Zhang <xiantao.zhang@...el.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Ralf Baechle <ralf@...ux-mips.org>, kvm@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] PF: Provide additional direct page notification


On 10.07.2013, at 12:48, Gleb Natapov wrote:

> On Wed, Jul 10, 2013 at 12:45:59PM +0200, Alexander Graf wrote:
>> 
>> On 10.07.2013, at 12:42, Gleb Natapov wrote:
>> 
>>> On Wed, Jul 10, 2013 at 12:39:01PM +0200, Alexander Graf wrote:
>>>> 
>>>> On 09.07.2013, at 18:01, Christian Borntraeger wrote:
>>>> 
>>>>> On 09/07/13 15:56, Dominik Dingel wrote:
>>>>>> By setting a Kconfig option, the architecture can control when
>>>>>> guest notifications will be presented by the apf backend.
>>>>>> So there is the default batch mechanism, working as before, where the vcpu thread
>>>>>> should pull in this information. On the other hand there is now the direct
>>>>>> mechanism, this will directly push the information to the guest.
>>>>>> 
>>>>>> Still the vcpu thread should call check_completion to cleanup leftovers,
>>>>>> that leaves most of the common code untouched.
>>>>>> 
>>>>>> Signed-off-by: Dominik Dingel <dingel@...ux.vnet.ibm.com>
>>>>> 
>>>>> Acked-by: Christian Borntraeger <borntraeger@...ibm.com> 
>>>>> for the "why". We want to use the existing architectured interface.
>>>> 
>>>> Shouldn't this be a runtime option?
>>>> 
>>> Why? What is the advantage of using sync delivery when HW can do it
>>> async?
>> 
>> What's the advantage of having an option at all then? Who selects it?
>> 
> x86 is stupid and cannot deliver the even asynchronously. Platform that
> can do it select the option.

We're in generic code. S390x enables it. X86 does not. That was the missing link!

Thanks a lot and sorry for the fuss :).


Alex

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