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Message-ID: <87zjch9gxj.fsf@rustcorp.com.au>
Date: Tue, 28 Oct 2014 10:57:52 +1030
From: Rusty Russell <rusty@...tcorp.com.au>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc: cornelia.huck@...ibm.com,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC 2/4] virtio_net: get rid of virtio_net_hdr/skb_vnet_hdr
"Michael S. Tsirkin" <mst@...hat.com> writes:
> virtio 1.0 doesn't use virtio_net_hdr anymore, and in fact, it's not
> really useful since virtio_net_hdr_mrg_rxbuf includes that as the first
> field anyway.
>
> Let's drop it, precalculate header len and store within vi instead.
>
> This way we can also remove struct skb_vnet_hdr.
Yes, this is definitely a win.
Acked-by: Rusty Russell <rusty@...tcorp.com.au>
Thanks,
Rusty.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> drivers/net/virtio_net.c | 88 ++++++++++++++++++++++--------------------------
> 1 file changed, 40 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 36f3dfc..a795a23 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -123,6 +123,9 @@ struct virtnet_info {
> /* Host can handle any s/g split between our header and packet data */
> bool any_header_sg;
>
> + /* Packet virtio header size */
> + u8 hdr_len;
> +
> /* Active statistics */
> struct virtnet_stats __percpu *stats;
>
> @@ -139,21 +142,14 @@ struct virtnet_info {
> struct notifier_block nb;
> };
>
> -struct skb_vnet_hdr {
> - union {
> - struct virtio_net_hdr hdr;
> - struct virtio_net_hdr_mrg_rxbuf mhdr;
> - };
> -};
> -
> struct padded_vnet_hdr {
> - struct virtio_net_hdr hdr;
> + struct virtio_net_hdr_mrg_rxbuf hdr;
> /*
> - * virtio_net_hdr should be in a separated sg buffer because of a
> - * QEMU bug, and data sg buffer shares same page with this header sg.
> - * This padding makes next sg 16 byte aligned after virtio_net_hdr.
> + * hdr is in a separate sg buffer, and data sg buffer shares same page
> + * with this header sg. This padding makes next sg 16 byte aligned
> + * after the header.
> */
> - char padding[6];
> + char padding[4];
> };
>
> /* Converting between virtqueue no. and kernel tx/rx queue no.
> @@ -179,9 +175,9 @@ static int rxq2vq(int rxq)
> return rxq * 2;
> }
>
> -static inline struct skb_vnet_hdr *skb_vnet_hdr(struct sk_buff *skb)
> +static inline struct virtio_net_hdr_mrg_rxbuf *skb_vnet_hdr(struct sk_buff *skb)
> {
> - return (struct skb_vnet_hdr *)skb->cb;
> + return (struct virtio_net_hdr_mrg_rxbuf *)skb->cb;
> }
>
> /*
> @@ -247,7 +243,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> unsigned int len, unsigned int truesize)
> {
> struct sk_buff *skb;
> - struct skb_vnet_hdr *hdr;
> + struct virtio_net_hdr_mrg_rxbuf *hdr;
> unsigned int copy, hdr_len, hdr_padded_len;
> char *p;
>
> @@ -260,13 +256,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>
> hdr = skb_vnet_hdr(skb);
>
> - if (vi->mergeable_rx_bufs) {
> - hdr_len = sizeof hdr->mhdr;
> - hdr_padded_len = sizeof hdr->mhdr;
> - } else {
> - hdr_len = sizeof hdr->hdr;
> + hdr_len = vi->hdr_len;
> + if (vi->mergeable_rx_bufs)
> + hdr_padded_len = sizeof *hdr;
> + else
> hdr_padded_len = sizeof(struct padded_vnet_hdr);
> - }
>
> memcpy(hdr, p, hdr_len);
>
> @@ -317,11 +311,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> return skb;
> }
>
> -static struct sk_buff *receive_small(void *buf, unsigned int len)
> +static struct sk_buff *receive_small(struct virtnet_info *vi, void *buf, unsigned int len)
> {
> struct sk_buff * skb = buf;
>
> - len -= sizeof(struct virtio_net_hdr);
> + len -= vi->hdr_len;
> skb_trim(skb, len);
>
> return skb;
> @@ -354,8 +348,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> unsigned int len)
> {
> void *buf = mergeable_ctx_to_buf_address(ctx);
> - struct skb_vnet_hdr *hdr = buf;
> - u16 num_buf = virtio16_to_cpu(rq->vq->vdev, hdr->mhdr.num_buffers);
> + struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> + u16 num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> struct page *page = virt_to_head_page(buf);
> int offset = buf - page_address(page);
> unsigned int truesize = max(len, mergeable_ctx_to_buf_truesize(ctx));
> @@ -373,8 +367,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> if (unlikely(!ctx)) {
> pr_debug("%s: rx error: %d buffers out of %d missing\n",
> dev->name, num_buf,
> - virtio16_to_cpu(rq->vq->vdev,
> - hdr->mhdr.num_buffers));
> + virtio16_to_cpu(vi->vdev,
> + hdr->num_buffers));
> dev->stats.rx_length_errors++;
> goto err_buf;
> }
> @@ -441,7 +435,7 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
> struct net_device *dev = vi->dev;
> struct virtnet_stats *stats = this_cpu_ptr(vi->stats);
> struct sk_buff *skb;
> - struct skb_vnet_hdr *hdr;
> + struct virtio_net_hdr_mrg_rxbuf *hdr;
>
> if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
> pr_debug("%s: short packet %i\n", dev->name, len);
> @@ -536,7 +530,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> gfp_t gfp)
> {
> struct sk_buff *skb;
> - struct skb_vnet_hdr *hdr;
> + struct virtio_net_hdr_mrg_rxbuf *hdr;
> int err;
>
> skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
> @@ -547,7 +541,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>
> hdr = skb_vnet_hdr(skb);
> sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
> - sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
> + sg_set_buf(rq->sg, hdr, vi->hdr_len);
> skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
>
> err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
> @@ -557,7 +551,8 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> return err;
> }
>
> -static int add_recvbuf_big(struct receive_queue *rq, gfp_t gfp)
> +static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
> + gfp_t gfp)
> {
> struct page *first, *list = NULL;
> char *p;
> @@ -588,8 +583,8 @@ static int add_recvbuf_big(struct receive_queue *rq, gfp_t gfp)
> p = page_address(first);
>
> /* rq->sg[0], rq->sg[1] share the same page */
> - /* a separated rq->sg[0] for virtio_net_hdr only due to QEMU bug */
> - sg_set_buf(&rq->sg[0], p, sizeof(struct virtio_net_hdr));
> + /* a separated rq->sg[0] for header - required in case !any_header_sg */
> + sg_set_buf(&rq->sg[0], p, vi->hdr_len);
>
> /* rq->sg[1] for data packet, from offset */
> offset = sizeof(struct padded_vnet_hdr);
> @@ -668,7 +663,7 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
> if (vi->mergeable_rx_bufs)
> err = add_recvbuf_mergeable(rq, gfp);
> else if (vi->big_packets)
> - err = add_recvbuf_big(rq, gfp);
> + err = add_recvbuf_big(vi, rq, gfp);
> else
> err = add_recvbuf_small(vi, rq, gfp);
>
> @@ -848,18 +843,14 @@ static void free_old_xmit_skbs(struct send_queue *sq)
>
> static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> {
> - struct skb_vnet_hdr *hdr;
> + struct virtio_net_hdr_mrg_rxbuf *hdr;
> const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
> struct virtnet_info *vi = sq->vq->vdev->priv;
> unsigned num_sg;
> - unsigned hdr_len;
> + unsigned hdr_len = vi->hdr_len;
> bool can_push;
>
> pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);
> - if (vi->mergeable_rx_bufs)
> - hdr_len = sizeof hdr->mhdr;
> - else
> - hdr_len = sizeof hdr->hdr;
>
> can_push = vi->any_header_sg &&
> !((unsigned long)skb->data & (__alignof__(*hdr) - 1)) &&
> @@ -867,7 +858,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> /* Even if we can, don't push here yet as this would skew
> * csum_start offset below. */
> if (can_push)
> - hdr = (struct skb_vnet_hdr *)(skb->data - hdr_len);
> + hdr = (struct virtio_net_hdr_mrg_rxbuf *)(skb->data - hdr_len);
> else
> hdr = skb_vnet_hdr(skb);
>
> @@ -902,7 +893,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> }
>
> if (vi->mergeable_rx_bufs)
> - hdr->mhdr.num_buffers = 0;
> + hdr->num_buffers = 0;
>
> sg_init_table(sq->sg, MAX_SKB_FRAGS + 2);
> if (can_push) {
> @@ -1773,18 +1764,19 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
> vi->mergeable_rx_bufs = true;
>
> + if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
> + vi->hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> + else
> + vi->hdr_len = sizeof(struct virtio_net_hdr);
> +
> if (virtio_has_feature(vdev, VIRTIO_F_ANY_LAYOUT))
> vi->any_header_sg = true;
>
> if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
> vi->has_cvq = true;
>
> - if (vi->any_header_sg) {
> - if (vi->mergeable_rx_bufs)
> - dev->needed_headroom = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> - else
> - dev->needed_headroom = sizeof(struct virtio_net_hdr);
> - }
> + if (vi->any_header_sg)
> + dev->needed_headroom = vi->hdr_len;
>
> /* Use single tx/rx queue pair as default */
> vi->curr_queue_pairs = 1;
> --
> MST
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