Re: [Qemu-devel] [virtio-dev] Re: [PATCH RFC] virtio-net: enable configurable tx queue size

[Jason Wang <jasowang@redhat.com>]

On 2017年05月22日 19:52, Wei Wang wrote:
> On 05/20/2017 04:42 AM, Michael S. Tsirkin wrote:
>> On Fri, May 19, 2017 at 10:32:19AM +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. The queue
>>> size specified by the user should be power of 2.
>>>
>>> Setting the tx queue size to be 1024 requires the guest driver to
>>> support the VIRTIO_NET_F_MAX_CHAIN_SIZE feature.
>> This should be a generic ring feature, not one specific to virtio net.
> OK. How about making two more changes below:
>
> 1) make the default tx queue size = 1024 (instead of 256).

As has been pointed out, you need compat the default value too in this case.

> We can reduce the size (to 256) if the MAX_CHAIN_SIZE feature
> is not supported by the guest.
> In this way, people who apply the QEMU patch can directly use the
> largest queue size(1024) without adding the booting command line.
>
> 2) The vhost backend does not use writev, so I think when the vhost
> backed is used, using 1024 queue size should not depend on the
> MAX_CHAIN_SIZE feature.

But do we need to consider even larger queue size now?

Btw, I think it's better to draft a spec patch.

Thanks

>
>
> Best,
> Wei