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Date: Thu, 25 Jan 2024 13:49:28 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: netdev@...r.kernel.org,
"Michael S. Tsirkin" <mst@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
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>,
virtualization@...ts.linux.dev,
bpf@...r.kernel.org,
Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH net-next 0/5] virtio-net: sq support premapped mode
On Thu, 25 Jan 2024 13:42:05 +0800, Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> On Thu, 25 Jan 2024 11:39:28 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Tue, Jan 16, 2024 at 3:59 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > This is the second part of virtio-net support AF_XDP zero copy.
> > >
> > > The whole patch set
> > > http://lore.kernel.org/all/20231229073108.57778-1-xuanzhuo@linux.alibaba.com
> > >
> > > ## About the branch
> > >
> > > This patch set is pushed to the net-next branch, but some patches are about
> > > virtio core. Because the entire patch set for virtio-net to support AF_XDP
> > > should be pushed to net-next, I hope these patches will be merged into net-next
> > > with the virtio core maintains's Acked-by.
> > >
> > > ============================================================================
> > >
> > > ## AF_XDP
> > >
> > > XDP socket(AF_XDP) is an excellent bypass kernel network framework. The zero
> > > copy feature of xsk (XDP socket) needs to be supported by the driver. The
> > > performance of zero copy is very good. mlx5 and intel ixgbe already support
> > > this feature, This patch set allows virtio-net to support xsk's zerocopy xmit
> > > feature.
> > >
> > > At present, we have completed some preparation:
> > >
> > > 1. vq-reset (virtio spec and kernel code)
> > > 2. virtio-core premapped dma
> > > 3. virtio-net xdp refactor
> > >
> > > So it is time for Virtio-Net to complete the support for the XDP Socket
> > > Zerocopy.
> > >
> > > Virtio-net can not increase the queue num at will, so xsk shares the queue with
> > > kernel.
> > >
> > > On the other hand, Virtio-Net does not support generate interrupt from driver
> > > manually, so when we wakeup tx xmit, we used some tips. If the CPU run by TX
> > > NAPI last time is other CPUs, use IPI to wake up NAPI on the remote CPU. If it
> > > is also the local CPU, then we wake up napi directly.
> > >
> > > This patch set includes some refactor to the virtio-net to let that to support
> > > AF_XDP.
> > >
> > > ## performance
> > >
> > > ENV: Qemu with vhost-user(polling mode).
> > > Host CPU: Intel(R) Xeon(R) Platinum 8163 CPU @ 2.50GHz
> > >
> > > ### virtio PMD in guest with testpmd
> > >
> > > testpmd> show port stats all
> > >
> > > ######################## NIC statistics for port 0 ########################
> > > RX-packets: 19531092064 RX-missed: 0 RX-bytes: 1093741155584
> > > RX-errors: 0
> > > RX-nombuf: 0
> > > TX-packets: 5959955552 TX-errors: 0 TX-bytes: 371030645664
> > >
> > >
> > > Throughput (since last show)
> > > Rx-pps: 8861574 Rx-bps: 3969985208
> > > Tx-pps: 8861493 Tx-bps: 3969962736
> > > ############################################################################
> > >
> > > ### AF_XDP PMD in guest with testpmd
> > >
> > > testpmd> show port stats all
> > >
> > > ######################## NIC statistics for port 0 ########################
> > > RX-packets: 68152727 RX-missed: 0 RX-bytes: 3816552712
> > > RX-errors: 0
> > > RX-nombuf: 0
> > > TX-packets: 68114967 TX-errors: 33216 TX-bytes: 3814438152
> > >
> > > Throughput (since last show)
> > > Rx-pps: 6333196 Rx-bps: 2837272088
> > > Tx-pps: 6333227 Tx-bps: 2837285936
> > > ############################################################################
> > >
> > > But AF_XDP consumes more CPU for tx and rx napi(100% and 86%).
> > >
> > > ## maintain
> > >
> > > I am currently a reviewer for virtio-net. I commit to maintain AF_XDP support in
> > > virtio-net.
> > >
> > > Please review.
> > >
> >
> > Rethink of the whole design, I have one question:
> >
> > The reason we need to store DMA information is to harden the virtqueue
> > to make sure the DMA unmap is safe. This seems redundant when the
> > buffer were premapped by the driver, for example:
> >
> > Receive queue maintains DMA information, so it doesn't need desc_extra to work.
> >
> > So can we simply
> >
> > 1) when premapping is enabled, store DMA information by driver itself
>
> YES. this is simpler. And this is more convenience.
> But the driver must allocate memory to store the dma info.
>
> > 2) don't store DMA information in desc_extra
>
> YES. But the desc_extra memory is wasted. The "next" item is used.
> Do you think should we free the desc_extra when the vq is premapped mode?
struct vring_desc_extra {
dma_addr_t addr; /* Descriptor DMA addr. */
u32 len; /* Descriptor length. */
u16 flags; /* Descriptor flags. */
u16 next; /* The next desc state in a list. */
};
The flags and the next are used whatever premapped or not.
So I think we can add a new array to store the addr and len.
If the vq is premappd, the memory can be freed.
struct vring_desc_extra {
u16 flags; /* Descriptor flags. */
u16 next; /* The next desc state in a list. */
};
struct vring_desc_dma {
dma_addr_t addr; /* Descriptor DMA addr. */
u32 len; /* Descriptor length. */
};
Thanks.
>
> Thanks.
>
>
> >
> > Would this be simpler?
> >
> > Thanks
> >
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