Re: [Qemu-devel] [virtio-dev] Re: [PATCH v2 1/2] virtio-net: enable configurable tx queue size

[Wei Wang <wei.w.wang@intel.com>]

On 06/22/2017 10:00 PM, Michael S. Tsirkin wrote:
> On Sat, Jun 17, 2017 at 04:38:03PM +0800, Wei Wang wrote:
>> On 06/16/2017 10:31 PM, Michael S. Tsirkin wrote:
>>> On Fri, Jun 16, 2017 at 06:48:38PM +0800, Wei Wang wrote:
>>>> This patch enables the virtio-net tx queue size to be configurable
>>>> between 256 (the default queue size) and 1024 by the user when the
>>>> vhost-user backend is used.
>>>>
>>>> Currently, the maximum tx queue size for other backends is 512 due
>>>> to the following limitations:
>>>> - QEMU backend: the QEMU backend implementation in some cases may
>>>> send 1024+1 iovs to writev.
>>>> - Vhost_net backend: there are possibilities that the guest sends
>>>> a vring_desc of memory which corsses a MemoryRegion thereby
>>>> generating more than 1024 iovs in total after translattion from
>>>> guest-physical address in the backend.
>>>>
>>>> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
>>>> ---
>>>>    hw/net/virtio-net.c            | 46 ++++++++++++++++++++++++++++++++++--------
>>>>    include/hw/virtio/virtio-net.h |  1 +
>>>>    2 files changed, 39 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>>> index 7d091c9..e1a08fd 100644
>>>> --- a/hw/net/virtio-net.c
>>>> +++ b/hw/net/virtio-net.c
>>>> @@ -33,8 +33,11 @@
>>>>    /* previously fixed value */
>>>>    #define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 256
>>>> +#define VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE 256
>>>> +
>>>>    /* for now, only allow larger queues; with virtio-1, guest can downsize */
>>>>    #define VIRTIO_NET_RX_QUEUE_MIN_SIZE VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE
>>>> +#define VIRTIO_NET_TX_QUEUE_MIN_SIZE VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE
>>>>    /*
>>>>     * Calculate the number of bytes up to and including the given 'field' of
>>>> @@ -1491,18 +1494,33 @@ static void virtio_net_tx_bh(void *opaque)
>>>>    static void virtio_net_add_queue(VirtIONet *n, int index)
>>>>    {
>>>>        VirtIODevice *vdev = VIRTIO_DEVICE(n);
>>>> +    NetClientState *nc = qemu_get_queue(n->nic);
>>>>        n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
>>>>                                               virtio_net_handle_rx);
>>>> +
>>>> +    /*
>>>> +     * Currently, backends other than vhost-user don't support 1024 queue
>>>> +     * size.
>>>> +     */
>>>> +    if (n->net_conf.tx_queue_size == VIRTQUEUE_MAX_SIZE &&
>>>> +        nc->peer->info->type != NET_CLIENT_DRIVER_VHOST_USER) {
>>>> +        fprintf(stderr, "warning: %s: queue size %d not supported\n",
>>>> +                __func__, n->net_conf.tx_queue_size);
>>>> +        n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
>>>> +    }
>>>> +
>>> Also, I suspect we can get here with no peer, and above will crash.
>>> It seems ugly to do this on each virtio_net_add_queue.
>>> How about moving this to realize?
>> The code has been re-arranged to make sure nc->peer is ready before
>> it's used, but I agree that it looks better to move the above to realize().
>>
>> Best,
>> Wei
> ping
>
> The issues left are minor, let's make progress and merge this asap
>

OK. I'll send out the new version soon.


Best,
Wei