From owner-svn-src-stable@freebsd.org Thu Oct 29 00:36:12 2015 Return-Path: Delivered-To: svn-src-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 0596AA1F849; Thu, 29 Oct 2015 00:36:12 +0000 (UTC) (envelope-from hiren@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id A25751326; Thu, 29 Oct 2015 00:36:11 +0000 (UTC) (envelope-from hiren@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id t9T0aA4C079187; Thu, 29 Oct 2015 00:36:10 GMT (envelope-from hiren@FreeBSD.org) Received: (from hiren@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id t9T0aAWE079186; Thu, 29 Oct 2015 00:36:10 GMT (envelope-from hiren@FreeBSD.org) Message-Id: <201510290036.t9T0aAWE079186@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: hiren set sender to hiren@FreeBSD.org using -f From: Hiren Panchasara Date: Thu, 29 Oct 2015 00:36:10 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r290125 - stable/10/sys/netinet X-SVN-Group: stable-10 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-stable@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for all the -stable branches of the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 29 Oct 2015 00:36:12 -0000 Author: hiren Date: Thu Oct 29 00:36:10 2015 New Revision: 290125 URL: https://svnweb.freebsd.org/changeset/base/290125 Log: MFC r289293 Fix an unnecessarily aggressive behavior where mtu clamping begins on first retransmission timeout (rto) when blackhole detection is enabled. Make sure it only happens when the second attempt to send the same segment also fails with rto. Also make sure that each mtu probing stage (usually 1448 -> 1188 -> 524) follows the same pattern and gets 2 chances (rto) before further clamping down. Note: RFC4821 doesn't specify implementation details on how this situation should be handled. Modified: stable/10/sys/netinet/tcp_timer.c Directory Properties: stable/10/ (props changed) Modified: stable/10/sys/netinet/tcp_timer.c ============================================================================== --- stable/10/sys/netinet/tcp_timer.c Thu Oct 29 00:18:03 2015 (r290124) +++ stable/10/sys/netinet/tcp_timer.c Thu Oct 29 00:36:10 2015 (r290125) @@ -617,9 +617,15 @@ tcp_timer_rexmt(void * xtp) int isipv6; #endif + /* + * Idea here is that at each stage of mtu probe (usually, 1448 + * -> 1188 -> 524) should be given 2 chances to recover before + * further clamping down. 'tp->t_rxtshift % 2 == 0' should + * take care of that. + */ if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) == (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) && - (tp->t_rxtshift <= 2)) { + (tp->t_rxtshift >= 2 && tp->t_rxtshift % 2 == 0)) { /* * Enter Path MTU Black-hole Detection mechanism: * - Disable Path MTU Discovery (IP "DF" bit). @@ -687,9 +693,11 @@ tcp_timer_rexmt(void * xtp) * with a lowered MTU, maybe this isn't a blackhole and * we restore the previous MSS and blackhole detection * flags. + * The limit '6' is determined by giving each probe + * stage (1448, 1188, 524) 2 chances to recover. */ if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) && - (tp->t_rxtshift > 4)) { + (tp->t_rxtshift > 6)) { tp->t_flags2 |= TF2_PLPMTU_PMTUD; tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE; optlen = tp->t_maxopd - tp->t_maxseg;