linux-kernel - Re: [PATCH v6 07/12] Add async PF initialization to PV guest.

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Message-ID: <20101006200520.GB4120@minantech.com>
Date:	Wed, 6 Oct 2010 22:05:20 +0200
From:	Gleb Natapov <gleb@...antech.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Gleb Natapov <gleb@...hat.com>, kvm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	hpa@...or.com, riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v6 07/12] Add async PF initialization to PV guest.

On Wed, Oct 06, 2010 at 11:45:12AM -0300, Marcelo Tosatti wrote:
> On Wed, Oct 06, 2010 at 12:55:04PM +0200, Gleb Natapov wrote:
> > On Tue, Oct 05, 2010 at 03:25:54PM -0300, Marcelo Tosatti wrote:
> > > On Mon, Oct 04, 2010 at 05:56:29PM +0200, Gleb Natapov wrote:
> > > > Enable async PF in a guest if async PF capability is discovered.
> > > > 
> > > > Signed-off-by: Gleb Natapov <gleb@...hat.com>
> > > > ---
> > > >  Documentation/kernel-parameters.txt |    3 +
> > > >  arch/x86/include/asm/kvm_para.h     |    5 ++
> > > >  arch/x86/kernel/kvm.c               |   92 +++++++++++++++++++++++++++++++++++
> > > >  3 files changed, 100 insertions(+), 0 deletions(-)
> > > > 
> > > 
> > > > +static int __cpuinit kvm_cpu_notify(struct notifier_block *self,
> > > > +				    unsigned long action, void *hcpu)
> > > > +{
> > > > +	int cpu = (unsigned long)hcpu;
> > > > +	switch (action) {
> > > > +	case CPU_ONLINE:
> > > > +	case CPU_DOWN_FAILED:
> > > > +	case CPU_ONLINE_FROZEN:
> > > > +		smp_call_function_single(cpu, kvm_guest_cpu_notify, NULL, 0);
> > > 
> > > wait parameter should probably be 1.
> > Why should we wait for it? FWIW I copied this from somewhere (May be
> > arch/x86/pci/amd_bus.c).
> 
> So that you know its executed in a defined point in cpu bringup.
> 
If I read code correctly CPU we are notified about is already running when
callback is called, so I do not see what waiting for IPI to be processed will
accomplish here. With many cpus we will make boot a little bit slower. I don't
care too much though, so if you still think that 1 is required here I'll make
it so. 

--
			Gleb.
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