netdev - Re: [PATCH net-next v2 06/13] virtio-net: rq submits premapped per-buffer

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Message-ID: <1730790584.4657414-1-xuanzhuo@linux.alibaba.com>
Date: Tue, 5 Nov 2024 15:09:44 +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>,
 Andrew Lunn <andrew+netdev@...n.ch>,
 "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 v2 06/13] virtio-net: rq submits premapped per-buffer

On Tue, 5 Nov 2024 11:23:50 +0800, Jason Wang <jasowang@...hat.com> wrote:
> On Wed, Oct 30, 2024 at 4:25 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> >
> > virtio-net rq submits premapped per-buffer by setting sg page to NULL;
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> >  drivers/net/virtio_net.c | 24 +++++++++++++-----------
> >  1 file changed, 13 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 792e9eadbfc3..09757fa408bd 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -542,6 +542,12 @@ static struct sk_buff *ptr_to_skb(void *ptr)
> >         return (struct sk_buff *)((unsigned long)ptr & ~VIRTIO_ORPHAN_FLAG);
> >  }
> >
> > +static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > +{
> > +       sg->dma_address = addr;
> > +       sg->length = len;
>
> This may work but I think it's better to reuse existing dma sg helpers like:
>
> sg_dma_address(sg) = addr;
> sg_dma_length(sg) = len;
>
> And we probably need to fix the virtio core which only uses
> sg_dma_address() but not sg_dma_length().
>
> This helps us to avoid future issues when CONFIG_NEED_SG_DMA_LENGTH is set.


I don't think so.

For no-premapped mode, we pass the sg as no-dma sg to virtio core,
so the virtio core uses the sg->length directly.
If virtio core do dma map for sg, we do not use the dma_mag_sg_attrs(),
so we must use sg->length directly.

In this case, for the driver, we can not use sg_dma_length(),
if CONFIG_NEED_SG_DMA_LENGTH is set, sg_dma_length() will set sg->dma_length,
but virtio core use sg->length.

For sg->dma_address, it is ok for me to use sg_dma_address or not.
But for consistency to sg->length, I use the sg->dma_address directly.

I noticed this is special, so I put them into an independent function.

Thanks.

>
> Others look good.
>
> Thanks
>
> > +}
> > +
> >  static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
> >                             bool in_napi, struct virtnet_sq_free_stats *stats)
> >  {
> > @@ -915,8 +921,7 @@ static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
> >         addr = dma->addr - sizeof(*dma) + offset;
> >
> >         sg_init_table(rq->sg, 1);
> > -       rq->sg[0].dma_address = addr;
> > -       rq->sg[0].length = len;
> > +       sg_fill_dma(rq->sg, addr, len);
> >  }
> >
> >  static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
> > @@ -1068,12 +1073,6 @@ static void check_sq_full_and_disable(struct virtnet_info *vi,
> >         }
> >  }
> >
> > -static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > -{
> > -       sg->dma_address = addr;
> > -       sg->length = len;
> > -}
> > -
> >  static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi,
> >                                    struct receive_queue *rq, void *buf, u32 len)
> >  {
> > @@ -1354,7 +1353,8 @@ static int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct receive_queue
> >                 sg_init_table(rq->sg, 1);
> >                 sg_fill_dma(rq->sg, addr, len);
> >
> > -               err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, xsk_buffs[i], gfp);
> > +               err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, xsk_buffs[i],
> > +                                                   NULL, true, gfp);
> >                 if (err)
> >                         goto err;
> >         }
> > @@ -2431,7 +2431,8 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> >
> >         virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
> >
> > -       err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > +       err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx,
> > +                                           rq->do_dma, gfp);
> >         if (err < 0) {
> >                 if (rq->do_dma)
> >                         virtnet_rq_unmap(rq, buf, 0);
> > @@ -2546,7 +2547,8 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> >         virtnet_rq_init_one_sg(rq, buf, len);
> >
> >         ctx = mergeable_len_to_ctx(len + room, headroom);
> > -       err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > +       err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx,
> > +                                           rq->do_dma, gfp);
> >         if (err < 0) {
> >                 if (rq->do_dma)
> >                         virtnet_rq_unmap(rq, buf, 0);
> > --
> > 2.32.0.3.g01195cf9f
> >
>