netdev - Re: [RFC PATCH V2 3/3] Ixgbevf: Add migration support for ixgbevf driver

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Date:	Wed, 25 Nov 2015 14:28:05 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	a.motakis@...tualopensystems.com, alex.williamson@...hat.com,
	b.reynal@...tualopensystems.com, bhelgaas@...gle.com,
	carolyn.wyborny@...el.com, donald.c.skidmore@...el.com,
	eddie.dong@...el.com, nrupal.jani@...el.com, agraf@...e.de,
	kvm@...r.kernel.org, pbonzini@...hat.com, qemu-devel@...gnu.org,
	emil.s.tantilov@...el.com, gerlitz.or@...il.com,
	mark.d.rustad@...el.com, eric.auger@...aro.org,
	intel-wired-lan@...ts.osuosl.org, jeffrey.t.kirsher@...el.com,
	jesse.brandeburg@...el.com, john.ronciak@...el.com,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	matthew.vick@...el.com, mitch.a.williams@...el.com,
	netdev@...r.kernel.org, shannon.nelson@...el.com,
	weiyang@...ux.vnet.ibm.com, zajec5@...il.com
Subject: Re: [RFC PATCH V2 3/3] Ixgbevf: Add migration support for ixgbevf
 driver

On Wed, Nov 25, 2015 at 01:39:32PM +0800, Lan Tianyu wrote:
> On 2015年11月25日 05:20, Michael S. Tsirkin wrote:
> > I have to say, I was much more interested in the idea
> > of tracking dirty memory. I have some thoughts about
> > that one - did you give up on it then?
> 
> No, our finial target is to keep VF active before doing
> migration and tracking dirty memory is essential. But this
> seems not easy to do that in short term for upstream. As
> starters, stop VF before migration.

Frankly, I don't really see what this short term hack buys us,
and if it goes in, we'll have to maintain it forever.

Also, assuming you just want to do ifdown/ifup for some reason, it's
easy enough to do using a guest agent, in a completely generic way.


> After deep thinking, the way of stopping VF still needs tracking
> DMA-accessed dirty memory to make sure the received data buffer
> before stopping VF migrated. It's easier to do that via dummy writing
> data buffer when receive packet.
> 
> 
> -- 
> Best regards
> Tianyu Lan
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