Re: [Qemu-devel] live migration vs device assignment (motivation)

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Dec 29, 2015 at 01:42:14AM +0800, Lan, Tianyu wrote:
> 
> 
> On 12/25/2015 8:11 PM, Michael S. Tsirkin wrote:
> >As long as you keep up this vague talk about performance during
> >migration, without even bothering with any measurements, this patchset
> >will keep going nowhere.
> >
> 
> I measured network service downtime for "keep device alive"(RFC patch V1
> presented) and "put down and up network interface"(RFC patch V2 presented)
> during migration with some optimizations.
> 
> The former is around 140ms and the later is around 240ms.
> 
> My patchset relies on the maibox irq which doesn't work in the suspend state
> and so can't get downtime for suspend/resume cases. Will try to get the
> result later.


Interesting. So you sare saying merely ifdown/ifup is 100ms?
This does not sound reasonable.
Is there a chance you are e.g. getting IP from dhcp?

If so that is wrong - clearly should reconfigure the old IP
back without playing with dhcp. For testing, just set up
a static IP.

> >
> >
> >
> >There's Alex's patch that tracks memory changes during migration.  It
> >needs some simple enhancements to be useful in production (e.g. add a
> >host/guest handshake to both enable tracking in guest and to detect the
> >support in host), then it can allow starting migration with an assigned
> >device, by invoking hot-unplug after most of memory have been migrated.
> >
> >Please implement this in qemu and measure the speed.
> 
> Sure. Will do that.
> 
> >I will not be surprised if destroying/creating netdev in linux
> >turns out to take too long, but before anyone bothered
> >checking, it does not make sense to discuss further enhancements.