On 11/28/2018 04:16 AM, Yafang Shao wrote:
> When walk RB tree, we'd better use skb_rbtree_walk* helpers, that can make
> the code more clear.
> As skb_rbtree_walk() can't be used in tcp_clean_rtx_queue(), so the new
> helper skb_rbtree_walk_safe() is introduced.
This makes things slower. Let me explain inline.
>
> Signed-off-by: Yafang Shao <laoar.s...@gmail.com>
> ---
> include/linux/skbuff.h | 5 +++++
> net/ipv4/tcp_input.c | 5 ++---
> 2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 73902ac..37ff792 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -3256,6 +3256,11 @@ static inline int __skb_grow_rcsum(struct sk_buff
> *skb, unsigned int len)
> for (skb = skb_rb_first(root); skb != NULL;
> \
> skb = skb_rb_next(skb))
>
> +#define skb_rbtree_walk_safe(skb, root, tmp)
> \
> + for (skb = skb_rb_first(root);
> \
> + tmp = skb ? skb_rb_next(skb) : NULL, skb != NULL;
> \
> + skb = tmp)
> +
> #define skb_rbtree_walk_from(skb)
> \
> for (; skb != NULL;
> \
> skb = skb_rb_next(skb))
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index f323978..ab6add2 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3043,7 +3043,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, u32
> prior_fack,
> struct tcp_sock *tp = tcp_sk(sk);
> u32 prior_sacked = tp->sacked_out;
> u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
> - struct sk_buff *skb, *next;
> + struct sk_buff *skb, *tmp;
> bool fully_acked = true;
> long sack_rtt_us = -1L;
> long seq_rtt_us = -1L;
> @@ -3055,7 +3055,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, u32
> prior_fack,
>
> first_ackt = 0;
>
> - for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
> + skb_rbtree_walk_safe(skb, &sk->tcp_rtx_queue, tmp) {
> struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
> const u32 start_seq = scb->seq;
> u8 sacked = scb->sacked;
> @@ -3126,7 +3126,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, u32
> prior_fack,
> if (!fully_acked)
> break;
>
> - next = skb_rb_next(skb);
We call skb_rb_next() here only, not at the beginning of the loop.
Why ?
Because we can break of the loop if the current skb is not fully acked.
So your patch would add unnecessary overhead, since the extra sk_rb_next()
could add more extra cache line misses.
