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Message-ID: <CACGkMEv_MOMHz1U48aVPXSj9gVJqA_h-UDt+oNgVgCQww4Jbdg@mail.gmail.com>
Date: Mon, 1 Jul 2024 11:20:33 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.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 v6 08/10] virtio_net: xsk: rx: support recv small mode
On Fri, Jun 28, 2024 at 1:48 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Fri, 28 Jun 2024 10:19:41 +0800, Jason Wang <jasowang@...hat.com> wrote:
> > On Tue, Jun 18, 2024 at 3:57 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> > >
> > > In the process:
> > > 1. We may need to copy data to create skb for XDP_PASS.
> > > 2. We may need to call xsk_buff_free() to release the buffer.
> > > 3. The handle for xdp_buff is difference from the buffer.
> > >
> > > If we pushed this logic into existing receive handle(merge and small),
> > > we would have to maintain code scattered inside merge and small (and big).
> > > So I think it is a good choice for us to put the xsk code into an
> > > independent function.
> >
> > I think it's better to try to reuse the existing functions.
> >
> > More below:
> >
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > > ---
> > > drivers/net/virtio_net.c | 135 ++++++++++++++++++++++++++++++++++++++-
> > > 1 file changed, 133 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index 2ac5668a94ce..06608d696e2e 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -500,6 +500,10 @@ struct virtio_net_common_hdr {
> > > };
> > >
> > > static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> > > +static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > > + struct net_device *dev,
> > > + unsigned int *xdp_xmit,
> > > + struct virtnet_rq_stats *stats);
> > >
> > > static bool is_xdp_frame(void *ptr)
> > > {
> > > @@ -1040,6 +1044,120 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> > > sg->length = len;
> > > }
> > >
> > > +static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi,
> > > + struct receive_queue *rq, void *buf, u32 len)
> > > +{
> > > + struct xdp_buff *xdp;
> > > + u32 bufsize;
> > > +
> > > + xdp = (struct xdp_buff *)buf;
> > > +
> > > + bufsize = xsk_pool_get_rx_frame_size(rq->xsk.pool) + vi->hdr_len;
> > > +
> > > + if (unlikely(len > bufsize)) {
> > > + pr_debug("%s: rx error: len %u exceeds truesize %u\n",
> > > + vi->dev->name, len, bufsize);
> > > + DEV_STATS_INC(vi->dev, rx_length_errors);
> > > + xsk_buff_free(xdp);
> > > + return NULL;
> > > + }
> > > +
> > > + xsk_buff_set_size(xdp, len);
> > > + xsk_buff_dma_sync_for_cpu(xdp);
> > > +
> > > + return xdp;
> > > +}
> > > +
> > > +static struct sk_buff *xdp_construct_skb(struct receive_queue *rq,
> > > + struct xdp_buff *xdp)
> > > +{
> >
> > So we have a similar caller which is receive_small_build_skb(). Any
> > chance to reuse that?
>
> receive_small_build_skb works with build_skb.
RIght.
>
> Here we need to copy the packet from the xsk buffer to the skb buffer.
> So I do not think we can reuse it.
>
Let's rename this to xsk_construct_skb() ?
>
> >
> > > + unsigned int metasize = xdp->data - xdp->data_meta;
> > > + struct sk_buff *skb;
> > > + unsigned int size;
> > > +
> > > + size = xdp->data_end - xdp->data_hard_start;
> > > + skb = napi_alloc_skb(&rq->napi, size);
> > > + if (unlikely(!skb)) {
> > > + xsk_buff_free(xdp);
> > > + return NULL;
> > > + }
> > > +
> > > + skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
> > > +
> > > + size = xdp->data_end - xdp->data_meta;
> > > + memcpy(__skb_put(skb, size), xdp->data_meta, size);
> > > +
> > > + if (metasize) {
> > > + __skb_pull(skb, metasize);
> > > + skb_metadata_set(skb, metasize);
> > > + }
> > > +
> > > + xsk_buff_free(xdp);
> > > +
> > > + return skb;
> > > +}
> > > +
> > > +static struct sk_buff *virtnet_receive_xsk_small(struct net_device *dev, struct virtnet_info *vi,
> > > + struct receive_queue *rq, struct xdp_buff *xdp,
> > > + unsigned int *xdp_xmit,
> > > + struct virtnet_rq_stats *stats)
> > > +{
> > > + struct bpf_prog *prog;
> > > + u32 ret;
> > > +
> > > + ret = XDP_PASS;
> > > + rcu_read_lock();
> > > + prog = rcu_dereference(rq->xdp_prog);
> > > + if (prog)
> > > + ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
> > > + rcu_read_unlock();
> > > +
> > > + switch (ret) {
> > > + case XDP_PASS:
> > > + return xdp_construct_skb(rq, xdp);
> > > +
> > > + case XDP_TX:
> > > + case XDP_REDIRECT:
> > > + return NULL;
> > > +
> > > + default:
> > > + /* drop packet */
> > > + xsk_buff_free(xdp);
> > > + u64_stats_inc(&stats->drops);
> > > + return NULL;
> > > + }
> > > +}
> > > +
> > > +static struct sk_buff *virtnet_receive_xsk_buf(struct virtnet_info *vi, struct receive_queue *rq,
> > > + void *buf, u32 len,
> > > + unsigned int *xdp_xmit,
> > > + struct virtnet_rq_stats *stats)
> > > +{
> > > + struct net_device *dev = vi->dev;
> > > + struct sk_buff *skb = NULL;
> > > + struct xdp_buff *xdp;
> > > +
> > > + len -= vi->hdr_len;
> > > +
> > > + u64_stats_add(&stats->bytes, len);
> > > +
> > > + xdp = buf_to_xdp(vi, rq, buf, len);
> > > + if (!xdp)
> > > + return NULL;
> > > +
> > > + if (unlikely(len < ETH_HLEN)) {
> > > + pr_debug("%s: short packet %i\n", dev->name, len);
> > > + DEV_STATS_INC(dev, rx_length_errors);
> > > + xsk_buff_free(xdp);
> > > + return NULL;
> > > + }
> > > +
> > > + if (!vi->mergeable_rx_bufs)
> > > + skb = virtnet_receive_xsk_small(dev, vi, rq, xdp, xdp_xmit, stats);
> > > +
> > > + return skb;
> > > +}
> > > +
> > > static int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct receive_queue *rq,
> > > struct xsk_buff_pool *pool, gfp_t gfp)
> > > {
> > > @@ -2363,9 +2481,22 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> > > void *buf;
> > > int i;
> > >
> > > - if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > - void *ctx;
> > > + if (rq->xsk.pool) {
> > > + struct sk_buff *skb;
> > > +
> > > + while (packets < budget) {
> > > + buf = virtqueue_get_buf(rq->vq, &len);
> > > + if (!buf)
> > > + break;
> > >
> > > + skb = virtnet_receive_xsk_buf(vi, rq, buf, len, xdp_xmit, &stats);
> > > + if (skb)
> > > + virtnet_receive_done(vi, rq, skb);
> > > +
> > > + packets++;
> > > + }
> >
> > If reusing turns out to be hard, I'd rather add new paths in receive_small().
>
> The exist function is called after virtnet_rq_get_buf(), that will do dma unmap.
> But for xsk, the dma unmap is not need. So xsk receive handle should use
> virtqueue_get_buf directly.
Probably but if it's just virtnet_rq_get_buf() we can simply did:
static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
{
void *buf;
buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
if (buf && rq->xsk.pool)
virtnet_rq_unmap(rq, buf, *len);
return buf;
}
Thanks
>
> Thanks.
>
> >
> > > + } else if (!vi->big_packets || vi->mergeable_rx_bufs) {
> > > + void *ctx;
> > > while (packets < budget &&
> > > (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > > receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> > > --
> > > 2.32.0.3.g01195cf9f
> > >
> >
> > Thanks
> >
>
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