netdev - Re: [PATCH net-next v5 12/15] virtio-net: support AF

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Date:   Thu, 17 Jun 2021 10:36:49 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org,
        "dust.li" <dust.li@...ux.alibaba.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 12/15] virtio-net: support AF_XDP zc tx


在 2021/6/16 下午8:57, Xuan Zhuo 写道:
> On Wed, 16 Jun 2021 20:51:41 +0800, Jason Wang <jasowang@...hat.com> wrote:
>> 在 2021/6/16 下午6:19, Xuan Zhuo 写道:
>>>>> + * In this way, even if xsk has been unbundled with rq/sq, or a new xsk and
>>>>> + * rq/sq  are bound, and a new virtnet_xsk_ctx_head is created. It will not
>>>>> + * affect the old virtnet_xsk_ctx to be recycled. And free all head and ctx when
>>>>> + * ref is 0.
>>>> This looks complicated and it will increase the footprint. Consider the
>>>> performance penalty and the complexity, I would suggest to use reset
>>>> instead.
>>>>
>>>> Then we don't need to introduce such context.
>>> I don't like this either. It is best if we can reset the queue, but then,
>>> according to my understanding, the backend should also be supported
>>> synchronously, so if you don't update the backend synchronously, you can't use
>>> xsk.
>>
>> Yes, actually, vhost-net support per vq suspending. The problem is that
>> we're lacking a proper API at virtio level.
>>
>> Virtio-pci has queue_enable but it forbids writing zero to that.
>>
>>
>>> I don’t think resetting the entire dev is a good solution. If you want to bind
>>> xsk to 10 queues, you may have to reset the entire device 10 times. I don’t
>>> think this is a good way. But the current spec does not support reset single
>>> queue, so I chose the current solution.
>>>
>>> Jason, what do you think we are going to do? Realize the reset function of a
>>> single queue?
>>
>> Yes, it's the best way. Do you want to work on that?
> Of course, I am very willing to continue this work. Although users must upgrade
> the backend to use virtio-net + xsk in the future, this makes the situation a
> bit troublesome.
>
> I will complete the kernel modification as soon as possible, but I am not
> familiar with the process of submitting the spec patch. Can you give me some
> guidance and where should I send the spec patch.


Subscribe the virtio dev mailing list [1] and send the spec path there.

Thanks

[1] 
https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio#feedback


>
> Thanks.
>
>> We can start from the spec patch, and introduce it as basic facility and
>> implement it in the PCI transport first.
>>
>> Thanks
>>
>>
>>> Looking forward to your reply!!!
>>>
>>> Thanks
>>>