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Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimiz

From: Li, Liang Z
Subject: Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization
Date: Fri, 4 Mar 2016 10:11:00 +0000

> On Fri, Mar 04, 2016 at 09:12:12AM +0000, Li, Liang Z wrote:
> > > Although I wonder which is cheaper; that would be fairly expensive
> > > for the guest wouldn't it? And you'd somehow have to kick the guest
> > > before migration to do the ballooning - and how long would you wait for
> it to finish?
> >
> > About 5 seconds for an 8G guest, balloon to 1G. Get the free pages
> > bitmap take about 20ms for an 8G idle guest.
> >
> > Liang
> Where is the time spent though? allocating within guest?
> Or passing the info to host?
> If the former, we can use existing inflate/deflate vqs:
> Have guest put each free page on inflate vq, then on deflate vq.

Maybe I am not clear enough.

I mean if we inflate balloon before live migration, for a 8GB guest, it takes 
about 5 Seconds for the inflating operation to finish.

For the PV solution, there is no need to inflate balloon before live migration, 
the only cost is to traversing the free_list to
 construct the free pages bitmap, and it takes about 20ms for a 8GB idle guest( 
less if there is less free pages),
 passing the free pages info to host will take about extra 3ms.

> --

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