From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] tcp: initialize max window for a new fastopen socket Date: Thu, 19 Jan 2017 11:41:03 -0500 (EST) Message-ID: <20170119.114103.1784185156530691440.davem@davemloft.net> References: <1484832999-1849-1-git-send-email-alexey.kodanev@oracle.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com, ycheng@google.com, ncardwell@google.com To: alexey.kodanev@oracle.com Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:59980 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753551AbdASQlF (ORCPT ); Thu, 19 Jan 2017 11:41:05 -0500 In-Reply-To: <1484832999-1849-1-git-send-email-alexey.kodanev@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Alexey Kodanev Date: Thu, 19 Jan 2017 16:36:39 +0300 > Found that if we run LTP netstress test with large MSS (65K), > the first attempt from server to send data comparable to this > MSS on fastopen connection will be delayed by the probe timer. > > Here is an example: > > < S seq 0:0 win 43690 options [mss 65495 wscale 7 tfo cookie] length 32 > > S. seq 0:0 ack 1 win 43690 options [mss 65495 wscale 7] length 0 > < . ack 1 win 342 length 0 > > Inside tcp_sendmsg(), tcp_send_mss() returns max MSS in 'mss_now', > as well as in 'size_goal'. This results the segment not queued for > transmition until all the data copied from user buffer. Then, inside > __tcp_push_pending_frames(), it breaks on send window test and > continues with the check probe timer. > > Fragmentation occurs in tcp_write_wakeup()... > > +0.2 > P. seq 1:43777 ack 1 win 342 length 43776 > < . ack 43777, win 1365 length 0 > > P. seq 43777:65001 ack 1 win 342 options [...] length 21224 > ... > > This also contradicts with the fact that we should bound to the half > of the window if it is large. > > Fix this flaw by correctly initializing max_window. Before that, it > could have large values that affect further calculations of 'size_goal'. > > Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path") > Signed-off-by: Alexey Kodanev Applied and queued up for -stable, thanks.