On Thu, Jan 25, 2024 at 1:52 PM Xuan Zhuo <[email protected]> wrote:
>
> On Thu, 25 Jan 2024 13:42:05 +0800, Xuan Zhuo <[email protected]>
> wrote:
> > On Thu, 25 Jan 2024 11:39:28 +0800, Jason Wang <[email protected]> wrote:
> > > On Tue, Jan 16, 2024 at 3:59 PM Xuan Zhuo <[email protected]>
> > > wrote:
> > > >
> > > > This is the second part of virtio-net support AF_XDP zero copy.
> > > >
> > > > The whole patch set
> > > > http://lore.kernel.org/all/[email protected]
> > > >
> > > > ## 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.
Right, and this looks like the common practice for most of the NIC drivers.
> >
> > > 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.
Yes.
> If the vq is premappd, the memory can be freed.
Then we need to make sure the premapped is set before find_vqs() etc.
>
> 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
>
> >
> > Thanks.
> >
> >
> > >
> > > Would this be simpler?
> > >
> > > Thanks
> > >
>
