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Date: Sun, 4 May 2014 14:41:05 -0700 From: Ji <lijimlee@...il.com> To: Weiping Pan <panweiping3@...il.com>, netdev@...r.kernel.org Subject: Re: Question about TLP patch Thanks, Weiping. As you found, I finally figured it out that it could be for "Recovery of any N-degree tail loss". However, I was actually testing with ER only (i,e, with TLP off, sysctl tcp_early_retrans =1) and loss pattern was "ALSL" ("S" means sacked, not 3-degree tail loss "ALLL"), and noticed ER behaves different from RFC5827. I understand that it may bring unnecessarily complexity in code if strictly following RFC5827 (early retransmit must be used only when "oseg - 1" segments have been SACKed) when TLP disabled. However, IMHO, a comment might be good for readers. Thanks, Ji Li On Sat, May 3, 2014 at 8:05 PM, Weiping Pan <panweiping3@...il.com> wrote: > On 04/24/2014 07:09 AM, Ji wrote: >> >> When reading the patch of Tail Loss Probe: >> >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ba8a3b19e764b6a65e4030ab0999be50c291e6c >> , I noticed this change: >> >> @@ -2321,7 +2322,7 @@ static bool tcp_time_to_recover(struct sock *sk, int >> flag) >> * interval if appropriate. >> */ >> if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out && >> - (tp->packets_out == (tp->sacked_out + 1) && tp->packets_out < 4) && >> + (tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) && >> !tcp_may_send_now(sk)) >> return !tcp_pause_early_retransmit(sk, flag); >> >> I think the original code is because of RFC5827 Early Retransmit for TCP, >> 3.2 >> "... When conditions (3.a) and (3.b) hold and a TCP connection does >> >> support SACK or SCTP is in use, Early Retransmit MUST be used only >> >> when "oseg - 1" segments have been SACKed...." >> >> With that change, it seems that the condition is relaxed. I wonder >> why it is so. Could you cast some lights on it? > > Please refer to > http://tools.ietf.org/html/draft-dukkipati-tcpm-tcp-loss-probe-01 > 4.2. Recovery of any N-degree tail loss > > thanks > Weiping Pan >> >> >> Thanks, >> Ji Li >> -- >> To unsubscribe from this list: send the line "unsubscribe netdev" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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