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Message-ID: <1679535924.6219428-2-xuanzhuo@linux.alibaba.com>
Date: Thu, 23 Mar 2023 09:45:24 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...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-foundation.org>, <bpf@...r.kernel.org>,
<netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 2/8] virtio_net: mergeable xdp: introduce mergeable_xdp_prepare
On Wed, 22 Mar 2023 19:52:48 +0800, Yunsheng Lin <linyunsheng@...wei.com> wrote:
> On 2023/3/22 11:03, Xuan Zhuo wrote:
> > Separating the logic of preparation for xdp from receive_mergeable.
> >
> > The purpose of this is to simplify the logic of execution of XDP.
> >
> > The main logic here is that when headroom is insufficient, we need to
> > allocate a new page and calculate offset. It should be noted that if
> > there is new page, the variable page will refer to the new page.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> > ---
> > drivers/net/virtio_net.c | 135 ++++++++++++++++++++++-----------------
> > 1 file changed, 77 insertions(+), 58 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 4d2bf1ce0730..bb426958cdd4 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -1162,6 +1162,79 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> > return 0;
> > }
> >
> > +static void *mergeable_xdp_prepare(struct virtnet_info *vi,
> > + struct receive_queue *rq,
> > + struct bpf_prog *xdp_prog,
> > + void *ctx,
> > + unsigned int *frame_sz,
> > + int *num_buf,
> > + struct page **page,
> > + int offset,
> > + unsigned int *len,
> > + struct virtio_net_hdr_mrg_rxbuf *hdr)
>
> The naming convention seems to be xdp_prepare_mergeable().
What convention?
>
> > +{
> > + unsigned int truesize = mergeable_ctx_to_truesize(ctx);
> > + unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> > + struct page *xdp_page;
> > + unsigned int xdp_room;
> > +
> > + /* Transient failure which in theory could occur if
> > + * in-flight packets from before XDP was enabled reach
> > + * the receive path after XDP is loaded.
> > + */
> > + if (unlikely(hdr->hdr.gso_type))
> > + return NULL;
> > +
> > + /* Now XDP core assumes frag size is PAGE_SIZE, but buffers
> > + * with headroom may add hole in truesize, which
> > + * make their length exceed PAGE_SIZE. So we disabled the
> > + * hole mechanism for xdp. See add_recvbuf_mergeable().
> > + */
> > + *frame_sz = truesize;
> > +
> > + /* This happens when headroom is not enough because
> > + * of the buffer was prefilled before XDP is set.
> > + * This should only happen for the first several packets.
> > + * In fact, vq reset can be used here to help us clean up
> > + * the prefilled buffers, but many existing devices do not
> > + * support it, and we don't want to bother users who are
> > + * using xdp normally.
> > + */
> > + if (!xdp_prog->aux->xdp_has_frags &&
> > + (*num_buf > 1 || headroom < virtnet_get_headroom(vi))) {
> > + /* linearize data for XDP */
> > + xdp_page = xdp_linearize_page(rq, num_buf,
> > + *page, offset,
> > + VIRTIO_XDP_HEADROOM,
> > + len);
> > +
> > + if (!xdp_page)
> > + return NULL;
> > + } else if (unlikely(headroom < virtnet_get_headroom(vi))) {
> > + xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
> > + sizeof(struct skb_shared_info));
> > + if (*len + xdp_room > PAGE_SIZE)
> > + return NULL;
> > +
> > + xdp_page = alloc_page(GFP_ATOMIC);
> > + if (!xdp_page)
> > + return NULL;
> > +
> > + memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM,
> > + page_address(*page) + offset, *len);
>
> It seems the above 'else if' was not really tested even before this patch,
> as there is no "--*num_buf" if xdp_linearize_page() is not called, which
> may causes virtnet_build_xdp_buff_mrg() to comsume one more buffer than
> expected?
Why do you think so?
>
> Also, it seems better to split the xdp_linearize_page() to two functions
> as pskb_expand_head() and __skb_linearize() do, one to expand the headroom,
> the other one to do the linearizing.
No skb here.
>
>
> > + } else {
> > + return page_address(*page) + offset;
> > + }
> > +
> > + *frame_sz = PAGE_SIZE;
> > +
> > + put_page(*page);
> > +
> > + *page = xdp_page;
> > +
> > + return page_address(xdp_page) + VIRTIO_XDP_HEADROOM;
> > +}
> > +
> > static struct sk_buff *receive_mergeable(struct net_device *dev,
> > struct virtnet_info *vi,
> > struct receive_queue *rq,
> > @@ -1181,7 +1254,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> > unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> > unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> > - unsigned int frame_sz, xdp_room;
> > + unsigned int frame_sz;
> > int err;
> >
> > head_skb = NULL;
> > @@ -1211,65 +1284,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > u32 act;
> > int i;
> >
> > - /* Transient failure which in theory could occur if
> > - * in-flight packets from before XDP was enabled reach
> > - * the receive path after XDP is loaded.
> > - */
> > - if (unlikely(hdr->hdr.gso_type))
> > + data = mergeable_xdp_prepare(vi, rq, xdp_prog, ctx, &frame_sz, &num_buf, &page,
> > + offset, &len, hdr);
> > + if (!data)
>
> unlikely().
Thanks.
>
> > goto err_xdp;
> >
> > - /* Now XDP core assumes frag size is PAGE_SIZE, but buffers
> > - * with headroom may add hole in truesize, which
> > - * make their length exceed PAGE_SIZE. So we disabled the
> > - * hole mechanism for xdp. See add_recvbuf_mergeable().
> > - */
> > - frame_sz = truesize;
> > -
> > - /* This happens when headroom is not enough because
> > - * of the buffer was prefilled before XDP is set.
> > - * This should only happen for the first several packets.
> > - * In fact, vq reset can be used here to help us clean up
> > - * the prefilled buffers, but many existing devices do not
> > - * support it, and we don't want to bother users who are
> > - * using xdp normally.
> > - */
> > - if (!xdp_prog->aux->xdp_has_frags &&
> > - (num_buf > 1 || headroom < virtnet_get_headroom(vi))) {
> > - /* linearize data for XDP */
> > - xdp_page = xdp_linearize_page(rq, &num_buf,
> > - page, offset,
> > - VIRTIO_XDP_HEADROOM,
> > - &len);
> > - frame_sz = PAGE_SIZE;
> > -
> > - if (!xdp_page)
> > - goto err_xdp;
> > - offset = VIRTIO_XDP_HEADROOM;
> > -
> > - put_page(page);
> > - page = xdp_page;
> > - } else if (unlikely(headroom < virtnet_get_headroom(vi))) {
> > - xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
> > - sizeof(struct skb_shared_info));
> > - if (len + xdp_room > PAGE_SIZE)
> > - goto err_xdp;
> > -
> > - xdp_page = alloc_page(GFP_ATOMIC);
> > - if (!xdp_page)
> > - goto err_xdp;
> > -
> > - memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM,
> > - page_address(page) + offset, len);
> > - frame_sz = PAGE_SIZE;
> > - offset = VIRTIO_XDP_HEADROOM;
> > -
> > - put_page(page);
> > - page = xdp_page;
> > - } else {
> > - xdp_page = page;
> > - }
> > -
> > - data = page_address(xdp_page) + offset;
> > err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> > &num_buf, &xdp_frags_truesz, stats);
> > if (unlikely(err))
> >
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