[Qemu-devel] vhost-user: current status of multiqueue support

[Nikita Kalyazin]

Hi,


What is the status of vhost-user multiqueue support in Qemu?

I am looking at 830d70db692e374b55555f4407f96a1ceefdcc97 patch in master and 
observe the following:
-8<-----------------------------------------------------------------------------
    case VHOST_SET_VRING_KICK:
    case VHOST_SET_VRING_CALL:
    case VHOST_SET_VRING_ERR:
        file = arg;
-       msg.u64 = file->index & VHOST_USER_VRING_IDX_MASK;
+       msg.u64 = (file->index + dev->vq_index) & VHOST_USER_VRING_IDX_MASK;
        msg.size = sizeof(m.u64);
        if (ioeventfd_enabled() && file->fd > 0) {
            fds[fd_num++] = file->fd;
        } else {
            msg.u64 |= VHOST_USER_VRING_NOFD_MASK;
        }
        break;
->8-----------------------------------------------------------------------------

What is the meaning of "file->index + dev->vq_index" expression?
Assuming "queues=4" parameter is passed at Qemu command line and "file->index" 
is either 0 or 1, Vhost receives the following sequence of VHOST_SET_VRING_CALL 
requests:
 - msg.u64 = 0 (file->index = 0, dev->vq_index = 0)
 - msg.u64 = 1 (file->index = 1, dev->vq_index = 0)
 - msg.u64 = 1 (file->index = 0, dev->vq_index = 1)
 - msg.u64 = 2 (file->index = 1, dev->vq_index = 1)
 - msg.u64 = 2 (file->index = 0, dev->vq_index = 2)
 - msg.u64 = 3 (file->index = 1, dev->vq_index = 2)
 - msg.u64 = 3 (file->index = 0, dev->vq_index = 3)
 - msg.u64 = 4 (file->index = 1, dev->vq_index = 3)
This means, CALLs for virtqueues 0-4 only would be configured (whereas 
virtqueues 5-7 remain unconfigured).

Has it been done intentionally?

-- 

Best regards,

Nikita Kalyazin,
address@hidden

Software Engineer
CE OS Group
Samsung R&D Institute Russia
Tel: +7 (495) 797-25-00 #3816
Tel: +7 (495) 797-25-03
Office #1501, 12-1, Dvintsev str.,
Moscow, 127018, Russia