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Re: [libvirt] [RFC PATCH] libvirt support to force convergence of live guest migration



On Wed, Jan 29, 2014 at 08:34:58 -0800, Chegu Vinod wrote:
> On 1/29/2014 8:27 AM, Jim Fehlig wrote:
> > Chegu Vinod wrote:
> >> Busy enterprise workloads hosted on large sized VM's tend to dirty
> >> memory faster than the transfer rate achieved via live guest migration.
> >> Despite some good recent improvements (& using dedicated 10Gig NICs
> >> between hosts) the live migration may NOT converge.
> >>
> >> Recently support was added in qemu (version 1.6) to allow a user to
> >> choose if they wish to force convergence of their migration via a
> >> new migration capability : "auto-converge". This feature allows for qemu
> >> to auto-detect lack of convergence and trigger a throttle-down of the
> >> VCPUs.
> >>
> >> This RFC patch includes the libvirt support needed to trigger this
> >> feature. (Testing is still in progress)
> >>    
> > Vinod,
> >
> > What is the status of this patch?  I see there were a few comments, but
> > don't see (or perhaps missed) a V2.
> 
> Thanks for your follow up query.
> 
> > Do you have time to continue working on this patch?  If not, I could
> > find some cycles to help out.  Thanks!
> Sorry for not responding...I have been busy with other things.
> 
> There were some minor comments on this specific patch. I can work with 
> you and address those soon.
> 
> But there is also another comment about having a new virsh interface to 
> allow for this capability to be changed during migration. I did look 
> into that but it requires a lot more changes in both libvirt and qemu 
> (qemu currently doesn't seem to support changing migration capabilities 
> once the migration has started... so we may have to defer that for now).

Oh, if qemu does not support that, we don't need the new APIs
naturally. It was not a hard requirement. Just that if qemu supported
it, we would like to support it too.

Jirka


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