netdev - Re: [PATCH vhost v11 05/10] virtio_ring: introduce virtqueue_dma

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Date: Wed, 2 Aug 2023 09:36:54 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Christoph Hellwig <hch@...radead.org>,
 virtualization@...ts.linux-foundation.org,
 "David S.  Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Paolo  Abeni <pabeni@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>,
 Daniel  Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John   Fastabend <john.fastabend@...il.com>,
 netdev@...r.kernel.org,
 bpf@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>,
 Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH vhost v11 05/10] virtio_ring: introduce virtqueue_dma_dev()

On Tue, 1 Aug 2023 08:45:10 -0700, Jakub Kicinski <kuba@...nel.org> wrote:
> On Tue, 1 Aug 2023 10:57:30 +0800 Xuan Zhuo wrote:
> > > You have this working and benchmarked or this is just and idea?
> >
> > This is not just an idea. I said that has been used on large scale.
> >
> > This is the library for the APP to use the AF_XDP. We has open it.
> > https://gitee.com/anolis/libxudp
> >
> > This is the Alibaba version of the nginx. That has been opened, that supported
> > to work with the libray to use AF_XDP.
> > http://tengine.taobao.org/
> >
> > I supported this on our kernel release Anolis/Alinux.
>
> Interesting!
>
> > The work was done about 2 years ago. You know, I pushed the first version to
> > enable AF_XDP on virtio-net about two years ago. I never thought the job would
> > be so difficult.
>
> Me neither, but it is what it is.
>
> > The nic (virtio-net) of AliYun can reach 24,000,000PPS.
> > So I think there is no different with the real HW on the performance.
> >
> > With the AF_XDP, the UDP pps is seven times that of the kernel udp stack.
>
> UDP pps or QUIC pps? UDP with or without GSO?

UDP PPS without GSO.

>
> Do you have measurements of how much it saves in real world workloads?
> I'm asking mostly out of curiosity, not to question the use case.

YES，the result is affected by the request size, we can reach 10-40%.
The smaller the request size, the lower the result.

>
> > > What about io_uring zero copy w/ pre-registered buffers.
> > > You'll get csum offload, GSO, all the normal perf features.
> >
> > We tried io-uring, but it was not suitable for our scenario.
> >
> > Yes, now the AF_XDP does not support the csum offload and GSO.
> > This is indeed a small problem.
>
> Can you say more about io-uring suitability? It can do zero copy
> and recently-ish Pavel optimized it quite a bit.

First, AF_XDP is also zero-copy. We also use XDP for a few things.

And this was all about two years ago, so we have to say something about io-uring
two years ago.

As far as I know, io-uring still use kernel udp stack, AF_XDP can
skip all kernel stack directly to driver.

So here, io-ring does not have too much advantage.

Thanks.