Re: [Qemu-devel] [PATCH V2 18/20] virtio-net: multiqueue support

[Aurelien Jarno]

On Wed, Apr 17, 2013 at 04:27:13PM +0800, Jason Wang wrote:
> On 04/17/2013 03:20 PM, Aurelien Jarno wrote:
> > On Tue, Apr 16, 2013 at 11:08:59AM +0800, Jason Wang wrote:
> >> On 04/15/2013 04:28 PM, Aurelien Jarno wrote:
> >>> On Mon, Apr 15, 2013 at 01:29:01PM +0800, Jason Wang wrote:
> >>>> On 04/13/2013 09:17 PM, Aurelien Jarno wrote:
> >>>>> On Fri, Jan 25, 2013 at 06:35:41PM +0800, Jason Wang wrote:
> >>>>>> This patch implements both userspace and vhost support for multiple 
> >>>>>> queue
> >>>>>> virtio-net (VIRTIO_NET_F_MQ). This is done by introducing an array of
> >>>>>> VirtIONetQueue to VirtIONet.
> >>>>>>
> >>>>>> Signed-off-by: Jason Wang <address@hidden>
> >>>>>> ---
> >>>>>>  hw/virtio-net.c |  317 
> >>>>>> +++++++++++++++++++++++++++++++++++++++++++------------
> >>>>>>  hw/virtio-net.h |   28 +++++-
> >>>>>>  2 files changed, 275 insertions(+), 70 deletions(-)
> >>>>> This patch breaks virtio-net in Minix, even with multiqueue disable. I
> >>>>> don't know virtio enough to know if it is a Minix or a QEMU problem.
> >>>>> However I have been able to identify the part of the commit causing the
> >>>>> failure:
> >>>> Hi Aurelien:
> >>>>
> >>>> Thanks for the work.
> >>>>>> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> >>>>>> index ef522d5..cec91a7 100644
> >>>>>> --- a/hw/virtio-net.c
> >>>>>> +++ b/hw/virtio-net.c
> >>>>> ...
> >>>>>
> >>>>>> +static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue, 
> >>>>>> int ctrl)
> >>>>>> +{
> >>>>>> +    VirtIODevice *vdev = &n->vdev;
> >>>>>> +    int i, max = multiqueue ? n->max_queues : 1;
> >>>>>> +
> >>>>>> +    n->multiqueue = multiqueue;
> >>>>>> +
> >>>>>> +    for (i = 2; i <= n->max_queues * 2 + 1; i++) {
> >>>>>> +        virtio_del_queue(vdev, i);
> >>>>>> +    }
> >>>>>> +
> >>>>> The for loop above is something which is new, even with multiqueue
> >>>>> disabled. Even with max_queues=1 it calls virtio_del_queue with i = 2
> >>>>> and i = 3. Disabling this loop makes the code to work as before.
> >>>> Looks like a bug here, need to change n->max_queues * 2 + 1 to
> >>>> n->max_queues * 2. The reason we need to del queue 2 each time because
> >>>> vq 2 has different meaning is multiqueue and single queue. In single
> >>>> queue, vq 2 maybe ctrl vq, but in multiqueue mode it was rx1.
> >>>>
> >>>> Let's see whether this small change works.
> >>> Unfortunately it doesn't fix the issue. I don't know a lot about virtio,
> >>> but would it be possible to only delete the queue that have been
> >>> enabled?
> >> The issue is vq 2 has different meanings in two modes, so it must be
> >> deleted and reinitialized during feature negotiation.
> >>>>> On the Minix side it triggers the following assertion:
> >>>>>
> >>>>> | virtio.c:370: assert "q->vaddr != NULL" failed, function 
> >>>>> "free_phys_queue"                                                       
> >>>>>                                                                         
> >>>>>   
> >>>>> | virtio_net(73141): panic: assert failed
> >>>>>
> >>>>> This correspond to this function in lib/libvirtio/virtio.c:
> >>>>>
> >>>>> | static void
> >>>>> | free_phys_queue(struct virtio_queue *q)
> >>>>> | {
> >>>>> |         assert(q != NULL);
> >>>>> |         assert(q->vaddr != NULL);
> >>>>> | 
> >>>>> |         free_contig(q->vaddr, q->ring_size);
> >>>>> |         q->vaddr = NULL;
> >>>>> |         q->paddr = 0;
> >>>>> |         q->num = 0;
> >>>>> |         free_contig(q->data, sizeof(q->data[0]));
> >>>>> |         q->data = NULL;
> >>>>> | }
> >>>>>
> >>>>> Do you have an idea if the problem is on the Minix side or on the QEMU
> >>>>> side?
> >>>>>
> >>>> Haven't figured out the relationship between virtqueue dynamic del/add
> >>>> and q->vaddr here. If the above changes does not work, I guess this
> >>> Unfortunately I don't really know the minix code either. I happen to
> >>> found the issue when testing other changes, and looked at the code to
> >>> try to understand the problem.
> >> Me too.
> >>>> problem happens only for ctrl vq (vq2)? And when does this happen?
> >>> I guess so given removing the call to virtio_del_queue() for vq2 fixes
> >>> or workarounds the issue.
> >> It will cause trouble for multiqueue guest who may think vq2 is rx queue.
> >>>> Rebooting?
> >>> It happens at the initial boot.
> >> Looks at the codes, looks like vq2 was initialized unconditionally at
> >> start, how about the following patch?
> >>
> >> diff --git a/hw/virtio-net.c b/hw/virtio-net.c
> >> index 4bb49eb..4886aa0 100644
> >> --- a/hw/virtio-net.c
> >> +++ b/hw/virtio-net.c
> >> @@ -1300,7 +1300,6 @@ VirtIODevice *virtio_net_init(DeviceState *dev,
> >> NICConf *conf,
> >>                                             virtio_net_handle_tx_bh);
> >>          n->vqs[0].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[0]);
> >>      }
> >> -    n->ctrl_vq = virtio_add_queue(&n->vdev, 64, virtio_net_handle_ctrl);
> >>      qemu_macaddr_default_if_unset(&conf->macaddr);
> >>      memcpy(&n->mac[0], &conf->macaddr, sizeof(n->mac));
> >>      n->status = VIRTIO_NET_S_LINK_UP;
> >>
> > Unfortunately this patch doesn't work, I tried it with and without your
> > previous suggested change (max_queues * 2 + 1) => max_queues * 2.
> >
> > Aurelien
> >
> 
> Thanks for the test, I will try to get a minix to see what happens and
> keep you updated.
> 

Thanks! I have used minix 3.2.1 which include virtio drivers. See the
following page, step 5 to know how to enable virtio:

http://wiki.minix3.org/en/UsersGuide/RunningOnQemu

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net