linux-kernel - Re: [PATCH] tcp: do not update snd_una if it is same with ack

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Date:   Sat, 03 Nov 2018 10:04:03 -0700
From:   Joe Perches <joe@...ches.com>
To:     Yafang Shao <laoar.shao@...il.com>, davem@...emloft.net,
        edumazet@...gle.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: do not update snd_una if it is same with ack_seq

On Sun, 2018-11-04 at 00:54 +0800, Yafang Shao wrote:
> In the slow path, TCP_SKB_SB(skb)->ack_seq may be same with tp->snd_una,
> and under this condition we don't need to update the snd_una.
> 
> Furthermore, tcp_ack_update_window() is only called in slow path,
> so introducing this check won't affect the fast path processing.
[]
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
[]
> @@ -3610,7 +3611,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
>  	if (flag & FLAG_UPDATE_TS_RECENT)
>  		tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
>  
> -	if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
> +	if (!(flag & FLAG_SLOWPATH) && flag & FLAG_SND_UNA_ADVANCED) {

stylistic nit:

While the precedence is correct in any case,
perhaps adding parentheses around
	flag & FLAG_SND_UNA_ADVANCED
would make it more obvious.