From owner-freebsd-bugs@FreeBSD.ORG Mon Nov 16 07:20:02 2009 Return-Path: Delivered-To: freebsd-bugs@hub.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 0DAB5106566C for ; Mon, 16 Nov 2009 07:20:02 +0000 (UTC) (envelope-from gnats@FreeBSD.org) Received: from freefall.freebsd.org (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx1.freebsd.org (Postfix) with ESMTP id C55528FC19 for ; Mon, 16 Nov 2009 07:20:01 +0000 (UTC) Received: from freefall.freebsd.org (localhost [127.0.0.1]) by freefall.freebsd.org (8.14.3/8.14.3) with ESMTP id nAG7K1Kp086517 for ; Mon, 16 Nov 2009 07:20:01 GMT (envelope-from gnats@freefall.freebsd.org) Received: (from gnats@localhost) by freefall.freebsd.org (8.14.3/8.14.3/Submit) id nAG7K1bV086516; Mon, 16 Nov 2009 07:20:01 GMT (envelope-from gnats) Resent-Date: Mon, 16 Nov 2009 07:20:01 GMT Resent-Message-Id: <200911160720.nAG7K1bV086516@freefall.freebsd.org> Resent-From: FreeBSD-gnats-submit@FreeBSD.org (GNATS Filer) Resent-To: freebsd-bugs@FreeBSD.org Resent-Reply-To: FreeBSD-gnats-submit@FreeBSD.org, Richard Scheffenegger Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2275E106566B for ; Mon, 16 Nov 2009 07:15:41 +0000 (UTC) (envelope-from nobody@FreeBSD.org) Received: from www.freebsd.org (www.freebsd.org [IPv6:2001:4f8:fff6::21]) by mx1.freebsd.org (Postfix) with ESMTP id 121A58FC1C for ; Mon, 16 Nov 2009 07:15:41 +0000 (UTC) Received: from www.freebsd.org (localhost [127.0.0.1]) by www.freebsd.org (8.14.3/8.14.3) with ESMTP id nAG7FeY3031472 for ; Mon, 16 Nov 2009 07:15:40 GMT (envelope-from nobody@www.freebsd.org) Received: (from nobody@localhost) by www.freebsd.org (8.14.3/8.14.3/Submit) id nAG7FeZ9031471; Mon, 16 Nov 2009 07:15:40 GMT (envelope-from nobody) Message-Id: <200911160715.nAG7FeZ9031471@www.freebsd.org> Date: Mon, 16 Nov 2009 07:15:40 GMT From: Richard Scheffenegger To: freebsd-gnats-submit@FreeBSD.org X-Send-Pr-Version: www-3.1 Cc: Subject: kern/140597: Lost Retransmission Detection X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 16 Nov 2009 07:20:02 -0000 >Number: 140597 >Category: kern >Synopsis: Lost Retransmission Detection >Confidential: no >Severity: serious >Priority: low >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Mon Nov 16 07:20:00 UTC 2009 >Closed-Date: >Last-Modified: >Originator: Richard Scheffenegger >Release: 8.0-RC2 >Organization: NetApp >Environment: FreeBSD rsFreeBSD.vie.demo 8.0-RC2 FreeBSD 8.0-RC2 #16: Sat Nov 14 22:25:28 CET 2009 root@rsFreeBSD.vie.demo:/usr/obj/usr/src/sys/GENERIC i386 >Description: SACK TCP in FreeBSD does not do Lost Retransmission Detection. Unlike linux, that functionality is not implemented, leading to a RTO when a single segment is lost twice. This reduces Goodput considerably during phases of higher congestion. See http://ubinet.yonsei.ac.kr/v2/publication/hpmn_papaers/ij/29.pdf And http://projects.itri.aist.go.jp/gnet/pfldnet08kodama.ppt >How-To-Repeat: Drop the same segment of a TCP Stram twice, when cwnd is open enough (3+ segments). >Fix: Simple fix is rather easy (doesn't work perfectly under all circumstances, but doesn't need new state variable and runs in constant time): When sending the last segment in a sackhole, store snd.max in rxmit. During SACK Ack processing, check the value of rxmit from the lowest hole against snd.fack; if snd.fack <= rxmit of that hole, set rxmit to start, and sackhint.nexthole == sackhole[0]. Care must be taken during hole-splitting (if rxmit > end of lower hole, set rxmit to snd.max), and all checks of sackhole[].rxmit need to deal with the signal rxmit > end. See http://www.ietf.org/mail-archive/web/tcpm/current/msg05003.html ff. >Release-Note: >Audit-Trail: >Unformatted: