On Wed, Nov 28, 2018 at 10:44 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
>
>
>
> 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.
>
I thought this extra sk_rb_next() doesn't add much overhead before,
since it won't take long time to execute.
Seems I made a mistake.
Thanks
Yafang
