Re: [PATCH net-next v2 3/3] xsk: build skb by page

[Magnus Karlsson <magnus.karlsson@gmail.com>]

On Wed, Jan 20, 2021 at 9:29 PM Alexander Lobakin <alobakin@pm.me> wrote:
>
> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> 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@linux.alibaba.com>
> > Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
> > ---
> >  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
>