Re: [Qemu-devel] [PATCH v3 1/2] virtio-net: enable configurable tx queue size

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

On 06/26/2017 11:18 AM, Jason Wang wrote:
>
> On 2017年06月23日 10:32, 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 after translattion from guest-physical
>> address in the backend.
>>
>> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
>> ---
>>   hw/net/virtio-net.c            | 45 
>> +++++++++++++++++++++++++++++++++---------
>>   include/hw/virtio/virtio-net.h |  1 +
>>   2 files changed, 37 insertions(+), 9 deletions(-)
>>
>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>> index 91eddaf..d13ca60 100644
>> --- a/hw/net/virtio-net.c
>> +++ b/hw/net/virtio-net.c
>> @@ -34,8 +34,11 @@
>>     /* previously fixed value */
>>   #define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 256
>> +
>> +    /*
>> +     * 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) {
>> +        n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
>
> Do we really want assume all vhost-user backend support 1024 queue size?
>

  Do you know any vhost-user backend implementation that doesn't support
1024 tx queue size?



>> +    }
>> +
>> +    for (i = 0; i < n->max_queues; i++) {
>> +        virtio_net_add_queue(n, i);
>> +    }
>
> Any reason to move virtio_net_add_queue() here?
>

Please check the whole init steps.  It was moved here (after qemu_new_nic())
to make sure nc->peer is not NULL.

Best,
Wei