Re: [PATCH net-next v2 3/3] xsk: build skb by page
From: Magnus Karlsson
Date: Thu Jan 21 2021 - 02:44:33 EST
On Wed, Jan 20, 2021 at 9:29 PM Alexander Lobakin <alobakin@xxxxx> wrote:
>
> From: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> Date: Wed, 20 Jan 2021 16:30:56 +0800
>
> > This patch is used to construct skb based on page to save memory copy
> > overhead.
> >
> > This function is implemented based on IFF_TX_SKB_NO_LINEAR. Only the
> > network card priv_flags supports IFF_TX_SKB_NO_LINEAR will use page to
> > directly construct skb. If this feature is not supported, it is still
> > necessary to copy data to construct skb.
> >
> > ---------------- Performance Testing ------------
> >
> > The test environment is Aliyun ECS server.
> > Test cmd:
> > ```
> > xdpsock -i eth0 -t -S -s <msg size>
> > ```
> >
> > Test result data:
> >
> > size 64 512 1024 1500
> > copy 1916747 1775988 1600203 1440054
> > page 1974058 1953655 1945463 1904478
> > percent 3.0% 10.0% 21.58% 32.3%
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
> > ---
> > net/xdp/xsk.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++----------
> > 1 file changed, 86 insertions(+), 18 deletions(-)
>
> Now I like the result, thanks!
>
> But Patchwork still display your series incorrectly (messages 0 and 1
> are missing). I'm concerning maintainers may not take this in such
> form. Try to pass the folder's name, not folder/*.patch to
> git send-email when sending, and don't use --in-reply-to when sending
> a new iteration.
Xuan,
Please make the new submission of the patch set a v3 even though you
did not change the code. Just so we can clearly see it is the new
submission.
> > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> > index 8037b04..40bac11 100644
> > --- a/net/xdp/xsk.c
> > +++ b/net/xdp/xsk.c
> > @@ -430,6 +430,87 @@ static void xsk_destruct_skb(struct sk_buff *skb)
> > sock_wfree(skb);
> > }
> >
> > +static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
> > + struct xdp_desc *desc)
> > +{
> > + u32 len, offset, copy, copied;
> > + struct sk_buff *skb;
> > + struct page *page;
> > + void *buffer;
> > + int err, i;
> > + u64 addr;
> > +
> > + skb = sock_alloc_send_skb(&xs->sk, 0, 1, &err);
> > + if (unlikely(!skb))
> > + return ERR_PTR(err);
> > +
> > + addr = desc->addr;
> > + len = desc->len;
> > +
> > + buffer = xsk_buff_raw_get_data(xs->pool, addr);
> > + offset = offset_in_page(buffer);
> > + addr = buffer - xs->pool->addrs;
> > +
> > + for (copied = 0, i = 0; copied < len; i++) {
> > + page = xs->pool->umem->pgs[addr >> PAGE_SHIFT];
> > +
> > + get_page(page);
> > +
> > + copy = min_t(u32, PAGE_SIZE - offset, len - copied);
> > +
> > + skb_fill_page_desc(skb, i, page, offset, copy);
> > +
> > + copied += copy;
> > + addr += copy;
> > + offset = 0;
> > + }
> > +
> > + skb->len += len;
> > + skb->data_len += len;
> > + skb->truesize += len;
> > +
> > + refcount_add(len, &xs->sk.sk_wmem_alloc);
> > +
> > + return skb;
> > +}
> > +
> > +static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> > + struct xdp_desc *desc)
> > +{
> > + struct sk_buff *skb = NULL;
> > +
> > + if (xs->dev->priv_flags & IFF_TX_SKB_NO_LINEAR) {
> > + skb = xsk_build_skb_zerocopy(xs, desc);
> > + if (IS_ERR(skb))
> > + return skb;
> > + } else {
> > + void *buffer;
> > + u32 len;
> > + int err;
> > +
> > + len = desc->len;
> > + skb = sock_alloc_send_skb(&xs->sk, len, 1, &err);
> > + if (unlikely(!skb))
> > + return ERR_PTR(err);
> > +
> > + skb_put(skb, len);
> > + buffer = xsk_buff_raw_get_data(xs->pool, desc->addr);
> > + err = skb_store_bits(skb, 0, buffer, len);
> > + if (unlikely(err)) {
> > + kfree_skb(skb);
> > + return ERR_PTR(err);
> > + }
> > + }
> > +
> > + skb->dev = xs->dev;
> > + skb->priority = xs->sk.sk_priority;
> > + skb->mark = xs->sk.sk_mark;
> > + skb_shinfo(skb)->destructor_arg = (void *)(long)desc->addr;
> > + skb->destructor = xsk_destruct_skb;
> > +
> > + return skb;
> > +}
> > +
> > static int xsk_generic_xmit(struct sock *sk)
> > {
> > struct xdp_sock *xs = xdp_sk(sk);
> > @@ -446,43 +527,30 @@ static int xsk_generic_xmit(struct sock *sk)
> > goto out;
> >
> > while (xskq_cons_peek_desc(xs->tx, &desc, xs->pool)) {
> > - char *buffer;
> > - u64 addr;
> > - u32 len;
> > -
> > if (max_batch-- == 0) {
> > err = -EAGAIN;
> > goto out;
> > }
> >
> > - len = desc.len;
> > - skb = sock_alloc_send_skb(sk, len, 1, &err);
> > - if (unlikely(!skb))
> > + skb = xsk_build_skb(xs, &desc);
> > + if (IS_ERR(skb)) {
> > + err = PTR_ERR(skb);
> > goto out;
> > + }
> >
> > - skb_put(skb, len);
> > - addr = desc.addr;
> > - buffer = xsk_buff_raw_get_data(xs->pool, addr);
> > - err = skb_store_bits(skb, 0, buffer, len);
> > /* This is the backpressure mechanism for the Tx path.
> > * Reserve space in the completion queue and only proceed
> > * if there is space in it. This avoids having to implement
> > * any buffering in the Tx path.
> > */
> > spin_lock_irqsave(&xs->pool->cq_lock, flags);
> > - if (unlikely(err) || xskq_prod_reserve(xs->pool->cq)) {
> > + if (xskq_prod_reserve(xs->pool->cq)) {
> > spin_unlock_irqrestore(&xs->pool->cq_lock, flags);
> > kfree_skb(skb);
> > goto out;
> > }
> > spin_unlock_irqrestore(&xs->pool->cq_lock, flags);
> >
> > - skb->dev = xs->dev;
> > - skb->priority = sk->sk_priority;
> > - skb->mark = sk->sk_mark;
> > - skb_shinfo(skb)->destructor_arg = (void *)(long)desc.addr;
> > - skb->destructor = xsk_destruct_skb;
> > -
> > err = __dev_direct_xmit(skb, xs->queue_id);
> > if (err == NETDEV_TX_BUSY) {
> > /* Tell user-space to retry the send */
> > --
> > 1.8.3.1
>
> Al
>