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

From: Yunsheng Lin
Date: Thu Jan 21 2021 - 05:58:55 EST

On 2021/1/21 15:41, Magnus Karlsson wrote:
> 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;

It seems the above init is unnecessary, for the skb is always
set before being used.

>>> +
>>> + 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
>>
>
> .
>