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

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Date:	Wed, 10 Jul 2013 13:48:43 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Alexander Graf <agraf@...e.de>
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 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.

--
			Gleb.
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