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

[Lan, Tianyu]

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.

> 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.