From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Thu, 21 Jan 2021 16:41:33 +0100
> On 1/21/21 2:47 PM, Xuan Zhuo wrote:
> > 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(-)
> >
> > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> > index 4a83117..38af7f1 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;
>
> This is not the truesize, unfortunately.
>
> We need to account for the number of pages, not number of bytes.
The easiest solution is:
skb->truesize += PAGE_SIZE * i;
i would be equal to skb_shinfo(skb)->nr_frags after exiting the loop.
> > +
> > + refcount_add(len, &xs->sk.sk_wmem_alloc);
> > +
> > + return skb;
> > +}
> > +
Al
