linux-kernel - RE: [RFC qemu 0/4] A PV solution for live migration optimization

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Date:	Thu, 10 Mar 2016 07:44:19 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Amit Shah <amit.shah@...hat.com>
CC:	"quintela@...hat.com" <quintela@...hat.com>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>
Subject: RE: [RFC qemu 0/4] A PV solution for live migration optimization

> > This patch set is the QEMU side implementation.
> >
> > The virtio-balloon is extended so that QEMU can get the free pages
> > information from the guest through virtio.
> >
> > After getting the free pages information (a bitmap), QEMU can use it
> > to filter out the guest's free pages in the ram bulk stage. This make
> > the live migration process much more efficient.
> >
> > This RFC version doesn't take the post-copy and RDMA into
> > consideration, maybe both of them can benefit from this PV solution by
> > with some extra modifications.
> 
> I like the idea, just have to prove (review) and test it a lot to ensure we don't
> end up skipping pages that matter.
> 
> However, there are a couple of points:
> 
> In my opinion, the information that's exchanged between the guest and the
> host should be exchanged over a virtio-serial channel rather than virtio-
> balloon.  First, there's nothing related to the balloon here.
> It just happens to be memory info.  Second, I would never enable balloon in
> a guest that I want to be performance-sensitive.  So even if you add this as
> part of balloon, you'll find no one is using this solution.
> 
> Secondly, I suggest virtio-serial, because it's meant exactly to exchange free-
> flowing information between a host and a guest, and you don't need to
> extend any part of the protocol for it (hence no changes necessary to the
> spec).  You can see how spice, vnc, etc., use virtio-serial to exchange data.
> 
> 
> 		Amit

Hi Amit,

 Could provide more information on how to use virtio-serial to exchange data?  Thread , Wiki or code are all OK. 
 I have not find some useful information yet.

Thanks
Liang