linux-kernel - Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit

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Date:   Tue, 5 Jan 2021 17:32:19 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org
Cc:     dust.li@...ux.alibaba.com, tonylu@...ux.alibaba.com,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        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>,
        "open list:VIRTIO CORE AND NET DRIVERS" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:XDP SOCKETS (AF_XDP)" <bpf@...r.kernel.org>
Subject: Re: [PATCH netdev 0/5] virtio-net support xdp socket zero copy xmit


On 2021/1/5 下午5:11, Xuan Zhuo wrote:
> The first patch made some adjustments to xsk.


Thanks a lot for the work. It's rather interesting.


>
> The second patch itself can be used as an independent patch to solve the problem
> that XDP may fail to load when the number of queues is insufficient.


It would be better to send this as a separated patch. Several people 
asked for this before.


>
> The third to last patch implements support for xsk in virtio-net.
>
> A practical problem with virtio is that tx interrupts are not very reliable.
> There will always be some missing or delayed tx interrupts. So I specially added
> a point timer to solve this problem. Of course, considering performance issues,
> The timer only triggers when the ring of the network card is full.


This is sub-optimal. We need figure out the root cause. We don't meet 
such issue before.

Several questions:

- is tx interrupt enabled?
- can you still see the issue if you disable event index?
- what's backend did you use? qemu or vhost(user)?


>
> Regarding the issue of virtio-net supporting xsk's zero copy rx, I am also
> developing it, but I found that the modification may be relatively large, so I
> consider this patch set to be separated from the code related to xsk zero copy
> rx.


That's fine, but a question here.

How is the multieuque being handled here. I'm asking since there's no 
programmable filters/directors support in virtio spec now.

Thanks


>
> Xuan Zhuo (5):
>    xsk: support get page for drv
>    virtio-net: support XDP_TX when not more queues
>    virtio-net, xsk: distinguish XDP_TX and XSK XMIT ctx
>    xsk, virtio-net: prepare for support xsk
>    virtio-net, xsk: virtio-net support xsk zero copy tx
>
>   drivers/net/virtio_net.c    | 643 +++++++++++++++++++++++++++++++++++++++-----
>   include/linux/netdevice.h   |   1 +
>   include/net/xdp_sock_drv.h  |  10 +
>   include/net/xsk_buff_pool.h |   1 +
>   net/xdp/xsk_buff_pool.c     |  10 +-
>   5 files changed, 597 insertions(+), 68 deletions(-)
>
> --
> 1.8.3.1
>