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

Xuan Zhuo
2024-11-05T07:23:08Z

On Tue, 5 Nov 2024 11:23:50 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Wed, Oct 30, 2024 at 4:25 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > virtio-net rq submits premapped per-buffer by setting sg page to NULL;
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.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
> >
>