From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Ricardo Leitner Subject: Re: TCP NewReno and single retransmit Date: Thu, 30 Oct 2014 09:24:06 -0200 Message-ID: <54521FD6.70403@redhat.com> References: <544E93BD.50202@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev , Yuchung Cheng , Eric Dumazet To: Neal Cardwell Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59664 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759273AbaJ3LYM (ORCPT ); Thu, 30 Oct 2014 07:24:12 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 30-10-2014 00:03, Neal Cardwell wrote: > On Mon, Oct 27, 2014 at 2:49 PM, Marcelo Ricardo Leitner > wrote: >> Hi, >> >> We have a report from a customer saying that on a very calm connection, like >> having only a single data packet within some minutes, if this packet gets to >> be re-transmitted, retrans_stamp is only cleared when the next acked packet >> is received. But this may make we abort the connection too soon if this next >> packet also gets lost, because the reference for the initial loss is still >> for a big while ago.. > ... >> @@ -2382,31 +2382,32 @@ static inline bool tcp_may_undo(const struct >> tcp_sock *tp) >> static bool tcp_try_undo_recovery(struct sock *sk) > ... >> if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { >> /* Hold old state until something *above* high_seq >> * is ACKed. For Reno it is MUST to prevent false >> * fast retransmits (RFC2582). SACK TCP is safe. */ >> tcp_moderate_cwnd(tp); >> + tp->retrans_stamp = 0; >> return true; >> } >> tcp_set_ca_state(sk, TCP_CA_Open); >> return false; >> } >> >> We would still hold state, at least part of it.. WDYT? > > This approach sounds OK to me as long as we include a check of > tcp_any_retrans_done(), as we do in the similar code paths (for > motivation, see the comment above tcp_any_retrans_done()). Yes, okay. I thought that this would be taken care of already by then but reading the code again now after your comment, I can see what you're saying. Thanks. > So it sounds fine to me if you change that one new line to the following 2: > > + if (!tcp_any_retrans_done(sk)) > + tp->retrans_stamp = 0; Will do. > Nice catch! A good part of it (including the diagram) was done by customer. :) I'll post the patch as soon as we sync with them (credits). Marcelo