Re: [libvirt] Question about save and restore OVS per-port data in live migration
-----Original Message-----
From: Michal Privoznik [mailto:mprivozn@redhat.com]
Sent: Wednesday, May 29, 2019 3:44 PM
To: wangxin (U) <wangxinxin.wang(a)huawei.com>; libvir-list(a)redhat.com
Cc: Lichunhe (Cloud Networking) <lichunhe(a)huawei.com>
Subject: Re: Question about save and restore OVS per-port data in live
migration
On 5/29/19 6:23 AM, wangxin (U) wrote:
> Hi
>
> When we try to migrate a guest with 12 NICs, we find libvirt will try
> to get per-port data in finish phase, it makes the guest paused for
> several hundred milliseconds.
>
> qemuMigrationCookieAddNetwork
> -> virNetDevOpenvswitchGetMigrateData for per-nic
> -> run 'ovs-vsctl --if-exists get Interface vnetx
external_ids:Port'
(about 25ms)
>
> In our case, there's no portData available and it seems there is no need to
run the cmd.
>
> Questions:
> 1. Is it necessary to get/set per-port data in migration finish phase? It will
increase the downtime.
> 2. Is there any way (i.e. a switch) to not run the OVS cmd if there's no
portData available?
>
IIUC migrating port data is required for openvswitch functionality on
the destination. Although looking at the commit that introduced this
does not say that explicitly (v1.0.0-rc1~8). But I vaguely recall that
being the case. We should revisit that decission and ask ovd guys if
that's still the case.
It will be helpful to do this.
And, is there a special reason to migrating port data in finish phase?
The finish phase should be as simple as possible.
Tanks,
Wangxin
Unfortunately, to libvirt 'port data' are opaque blob. And I'm not sure
we can know in advance what ports have data to transfer and which don't.
Michal