Re: How to impove downtime of Live-Migration caused bdrv_drain_all()

[张海斌 <xtay.haibin@gmail.com>]

Stefan Hajnoczi <stefanha@redhat.com> 于2019年3月29日周五 上午1:08写道：
>
> On Thu, Mar 28, 2019 at 05:53:34PM +0800, 张海斌 wrote:
> > hi, stefan
> >
> > I have faced the same problem you wrote in
> > https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg04025.html
> >
> > Reproduce as follow:
> > 1. Clone qemu code from https://git.qemu.org/git/qemu.git, add some
> > debug information and compile
> > 2. Start a new VM
> > 3. In VM, use fio randwrite to add pressure for disk
> > 4. Live migrate
> >
> > Log show as follow:
> > [2019-03-28 15:10:40.206] /data/qemu/cpus.c:1086: enter do_vm_stop
> > [2019-03-28 15:10:40.212] /data/qemu/cpus.c:1097: call bdrv_drain_all
> > [2019-03-28 15:10:40.989] /data/qemu/cpus.c:1099: call replay_disable_events
> > [2019-03-28 15:10:40.989] /data/qemu/cpus.c:1101: call bdrv_flush_all
> > [2019-03-28 15:10:41.004] /data/qemu/cpus.c:1104: done do_vm_stop
> >
> > Calling bdrv_drain_all() costs 792 mini-seconds.
> > I just add a bdrv_drain_all() at start of do_vm_stop() before
> > pause_all_vcpus(), but it doesn't work.
> > Is there any way to improve live-migration downtime cause by bdrv_drain_all()?
> >
> > haibin
>
> Thanks for your email.  Please send technical questions to
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>
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> answers that I give.
>
> Stefan