Re: [Qemu-devel] [PATCH] migration: optimize the downtime

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Jay Zhou (jianjay.zhou@huawei.com) wrote:
> Hi Dave,
> 
> On 2017/7/25 18:34, Dr. David Alan Gilbert wrote:
> > > After checking the codes of the newest libvirt, I think it is the same
> > > in the qemuMigrationWaitForCompletion function, which is used to poll
> > > qemu every 50ms.
> > 
> > Checking with Jiri Denemark (added to cc), newer libvirt should use
> > events when available - but that polling code is there to cope with
> > older qemu's.  So with a newer qemu, i think it should spot the
> > COMPLETED event.
> > 
> 
> I do tests on the newest libvirt(v3.6.0) + newest qemu(v2.9.90,
> v2.10.0-rc0-29-ga588c49-dirty). The log added indicates that the source
> side libvirt spots the COMPLETE event after the cleanup of the source side
> qemu, i.e. 300ms still exists.

OK, thanks for trying it.
I don't quite understand why in this case - migration_completion sets
the state to COMPLETE and I think that's done outside the lock and that
happens a bit before the retaking of the lock and then the call
to the savevm_state_cleanup;  so yes, thanks for doing the test.

> BTW, I'm not very familiar with libvirt, if there is something special to
> configure or I'm missing something, please let me know.

I don't think you should need to.

Dave

> Thanks,
> Jay
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK