netdev - Re: [PATCH net-next v5 08/15] virtio_net: sq support premapped mode

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Date: Mon, 17 Jun 2024 15:40:35 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.com>
Cc: netdev@...r.kernel.org,
 "Michael S. Tsirkin" <mst@...hat.com>,
 Eugenio Pérez <eperezma@...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
Subject: Re: [PATCH net-next v5 08/15] virtio_net: sq support premapped mode

On Mon, 17 Jun 2024 14:28:05 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Mon, Jun 17, 2024 at 1:00 PM Jason Wang <jasowang@...hat.com> wrote:
> >
> > On Fri, Jun 14, 2024 at 2:39 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > If the xsk is enabling, the xsk tx will share the send queue.
> > > But the xsk requires that the send queue use the premapped mode.
> > > So the send queue must support premapped mode when it is bound to
> > > af-xdp.
> > >
> > > * virtnet_sq_set_premapped(sq, true) is used to enable premapped mode.
> > >
> > >     In this mode, the driver will record the dma info when skb or xdp
> > >     frame is sent.
> > >
> > >     Currently, the SQ premapped mode is operational only with af-xdp. In
> > >     this mode, af-xdp, the kernel stack, and xdp tx/redirect will share
> > >     the same SQ. Af-xdp independently manages its DMA. The kernel stack
> > >     and xdp tx/redirect utilize this DMA metadata to manage the DMA
> > >     info.
> > >
>
> Note that there's indeed a mode when we have exclusive XDP TX queue:
>
>         /* XDP requires extra queues for XDP_TX */
>         if (curr_qp + xdp_qp > vi->max_queue_pairs) {
>                 netdev_warn_once(dev, "XDP request %i queues but max
> is %i. XDP_TX and XDP_REDIRECT will operate in a slower locked tx
> mode.\n",
>                                  curr_qp + xdp_qp, vi->max_queue_pairs);
>                 xdp_qp = 0;
>         }
>
> So we need to mention how the code works in this patch.

Sorry, I do not get it.

Could you say more?

Thanks.

>
> Thanks
>