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Subject: Re: [PATCH net-next] tcp: introduce skb_rbtree_walk_safe() and use it
 in tcp_clean_rtx_queue()
From:   Eric Dumazet <eric.dumazet@gmail.com>
To:     Yafang Shao <laoar.shao@gmail.com>, davem@davemloft.net,
        edumazet@google.com
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1543407379-3144-1-git-send-email-laoar.shao@gmail.com>
 <60467855-ea5f-3351-8b88-ffdfa60501e0@gmail.com>
Message-ID: <408125e7-bbb0-dcfb-ee19-58089802cac7@gmail.com>
Date:   Wed, 28 Nov 2018 08:53:58 -0800
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On 11/28/2018 06:44 AM, Eric Dumazet wrote:
> 

> 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 am testing the following optimization, since we can avoid the rb_next() call
when we reached snd_una

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f32397890b6dcbc34976954c4be142108efa04d8..6829e470f0c186a73c34dca414cd4a2b379baded 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3126,7 +3126,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
                if (!fully_acked)
                        break;
 
-               next = skb_rb_next(skb);
+               next = (scb->end_seq == tp->snd_una) ? NULL : skb_rb_next(skb);
+
                if (unlikely(skb == tp->retransmit_skb_hint))
                        tp->retransmit_skb_hint = NULL;
                if (unlikely(skb == tp->lost_skb_hint))