netdev - Re: a F-RTO question

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Message-ID: <CAJkE24+qgK4_cGtiEi6hWDFS2EVYPajHY3pigwh_RqguwsedNg@mail.gmail.com>
Date:	Wed, 28 Mar 2012 11:49:43 +0800
From:	Chao Pei <peichao85@...il.com>
To:	Li Yu <raise.sail@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: a F-RTO question

> Hi,
>
>        I have a question about tcp_process_frto(), the below source
> code :
>
> static int tcp_process_frto(struct sock *sk, int flag)
> {
>        .....
>
>        if (!before(tp->snd_una, tp->frto_highmark)) {
>                tcp_enter_frto_loss(sk, ...);
>                return 1;
>        }
>
>        .....
>
> }
>
>        As my understanding, the tp->frto_highmark likes tp->high_seq,
> it saves the seqno SND_NXT when a TCP connection enters F-RTO phase,
> is it the variable "recovery" in NewReno? So I think that if snd_una is
> equal with or after frto_highmark, which means peer ack new data, so
> why we enter Loss state here?
>
>        Thanks!
>
> Yu
>
>

If snd_una advances to frto_highmark, it is likely that the hole was
filled by the retransimitted packet, which means the original packet
was likely to have been lost.
So, we should enter loss state.
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