Re: [Qemu-devel] [PATCH v5] vhost-user: add multi queue support

[Maxime Leroy]

Hi Michael,

On Wed, Jul 8, 2015 at 4:29 PM, Michael S. Tsirkin <address@hidden> wrote:
> On Thu, May 28, 2015 at 09:23:06AM +0800, Ouyang Changchun wrote:
>> Based on patch by Nikolay Nikolaev:
>> Vhost-user will implement the multi queue support in a similar way
>> to what vhost already has - a separate thread for each queue.
>> To enable the multi queue functionality - a new command line parameter
>> "queues" is introduced for the vhost-user netdev.
>>
>> Signed-off-by: Nikolay Nikolaev <address@hidden>
>> Signed-off-by: Changchun Ouyang <address@hidden>
>
> So testing turned up a significant issue with the protocol extension in this
> one.  Specifically, remote has no idea how many queues guest actually
> wants to use (it's dynamic, guest changes this at any time).
> We need support for enabling and disabling queues dynamically.
>
> Given we are past hard freeze, and given no one uses this yet
> (dpdk upstream did not merge supporting protocol),
> I think the best thing to do is to disable this functionality for 2.4.
> I will send a patch to do this shortly.

You are making a wrong statement, we already use multiqueue for
vhost-user and we expected to have this support officially integrated
in qemu 2.4.

Libvirt 1.2.17 has been released with multiqueue support for
vhost-user. 
(http://libvirt.org/git/?p=libvirt.git;a=commit;h=366c22f2bcf1ddb8253c123f93fd18d1ba9eacd6)
It checks against the version of qemu (i.e. 2.4)  to know if
multiqueue is supported or not by qemu.
(http://libvirt.org/git/?p=libvirt.git;a=commitdiff;h=7971723b985b9adc27122a3503e7ab38ced2b57f;hp=e7f5510ef2d28ca0ae0ed5751b1fd3018130d6c1)

Dynamically enabling/disabling queue between host/guest is a nice
feature to have.
But it's not mandatory. You can still configure manually guest and
host to use the same number of queues.

I think this feature can be implemented later in qemu 2.5.

Regards,

Maxime