netdev - Re: [PATCH] tcp: remove useless update for flag parameter in tcp_enter_frto

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Message-ID: <CADVnQymQaCSKx0aRda6OiP=t2OToxHmvjXjYvTdxsq7oFE3DTg@mail.gmail.com>
Date:	Wed, 28 Mar 2012 01:29:02 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Li Yu <raise.sail@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: remove useless update for flag parameter in tcp_enter_frto_loss()

On Wed, Mar 28, 2012 at 12:23 AM, Li Yu <raise.sail@...il.com> wrote:
>
> It seem that we forget remove below two lines after copying code :)
>
> This update never impacts others.

The 'flag' variable will be used in later iterations of the
tcp_for_write_queue() loop. The comment seems to quite sensibly
indicate that the FLAG_DATA_ACKED bit is being set to avoid entering
that branch of the if statement in later segments in the loop:

2168                 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2169                         /* For some reason this R-bit might get cleared? */
2170                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2171                                 tp->retrans_out += tcp_skb_pcount(skb);
2172                         /* ...enter this if branch just for the
first segment */
2173                         flag |= FLAG_DATA_ACKED;
2174                 } else {

The structure of the logic seems intact from the original commit that
added this:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=d1a54c6a0a3f9c2c4ef71982d89b8571bd9eaa51

neal
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