From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net-next] tcp: ack immediately when a cwr packet arrives Date: Wed, 25 Jul 2018 16:21:38 -0700 (PDT) Message-ID: <20180725.162138.394671961252485113.davem@davemloft.net> References: <36385AF4-4EE4-4237-84B8-1978B091E28B@fb.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: brakmo@fb.com, ycheng@google.com, daniel@iogearbox.net, netdev@vger.kernel.org, Kernel-team@fb.com, ast@fb.com, eric.dumazet@gmail.com To: ncardwell@google.com Return-path: Received: from shards.monkeyblade.net ([23.128.96.9]:57664 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731640AbeGZAfm (ORCPT ); Wed, 25 Jul 2018 20:35:42 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: From: Neal Cardwell Date: Tue, 24 Jul 2018 21:57:27 -0400 > On Tue, Jul 24, 2018 at 1:42 PM Lawrence Brakmo wrote: >> >> Note that without this fix the 99% latencies when doing 10KB RPCs >> in a congested network using DCTCP are 40ms vs. 190us with the patch. >> Also note that these 40ms high tail latencies started after commit >> 3759824da87b30ce7a35b4873b62b0ba38905ef5 in Jul 2015, >> which triggered the bugs/features we are fixing/adding. I agree it is a >> debatable whether it is a bug fix or a feature improvement and I am >> fine either way. > > Good point. The fact that this greatly mitigates a regression in DCTCP > performance resulting from 3759824da87b30ce7a35b4873b62b0ba38905ef5 > ("tcp: PRR uses CRB mode by default and SS mode conditionally") IMHO > seems to be a good argument for putting this patch ("tcp: ack > immediately when a cwr packet arrives") in the "net" branch and stable > releases. Thus, applied to 'net' and queued up for -stable.