From mboxrd@z Thu Jan 1 00:00:00 1970 From: Damian Lukowski Subject: [PATCH 2/2] RTO connection timeout: sysctl documentation update Date: Tue, 01 Sep 2009 22:24:04 +0200 Message-ID: <4A9D82E4.6050709@tvk.rwth-aachen.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7BIT To: Netdev Return-path: Received: from mta-2.ms.rz.RWTH-Aachen.DE ([134.130.7.73]:54558 "EHLO mta-2.ms.rz.rwth-aachen.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754277AbZIAUYI (ORCPT ); Tue, 1 Sep 2009 16:24:08 -0400 Received: from ironport-out-1.rz.rwth-aachen.de ([134.130.5.40]) by mta-2.ms.rz.RWTH-Aachen.de (Sun Java(tm) System Messaging Server 6.3-7.04 (built Sep 26 2008)) with ESMTP id <0KPB0097C7BWNDB0@mta-2.ms.rz.RWTH-Aachen.de> for netdev@vger.kernel.org; Tue, 01 Sep 2009 22:24:04 +0200 (CEST) Received: from [137.226.143.131] (nexus.tvk.RWTH-Aachen.DE [137.226.143.131]) by relay.rwth-aachen.de (8.13.8+Sun/8.13.8/1) with ESMTP id n81KO4fG004394 for ; Tue, 01 Sep 2009 22:24:04 +0200 (CEST) Sender: netdev-owner@vger.kernel.org List-ID: This patch updates the sysctl documentation concerning the interpretation of tcp_retries{1,2} and tcp_orphan_retries. Signed-off-by: Damian Lukowski --- Documentation/networking/ip-sysctl.txt | 37 ++++++++++++++++++++++--------- 1 files changed, 26 insertions(+), 11 deletions(-) diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 8be7623..b6ee71f 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -311,9 +311,12 @@ tcp_no_metrics_save - BOOLEAN connections. tcp_orphan_retries - INTEGER - How may times to retry before killing TCP connection, closed - by our side. Default value 7 corresponds to ~50sec-16min - depending on RTO. If you machine is loaded WEB server, + This value influences the timeout of a locally closed TCP connection, + when RTO retransmissions remain unacknowledged. + See tcp_retries2 for more details. + + The default value is 7. + If your machine is a loaded WEB server, you should think about lowering this value, such sockets may consume significant resources. Cf. tcp_max_orphans. @@ -327,16 +330,28 @@ tcp_retrans_collapse - BOOLEAN certain TCP stacks. tcp_retries1 - INTEGER - How many times to retry before deciding that something is wrong - and it is necessary to report this suspicion to network layer. - Minimal RFC value is 3, it is default, which corresponds - to ~3sec-8min depending on RTO. + This value influences the time, after which TCP decides, that + something is wrong due to unacknowledged RTO retransmissions, + and reports this suspicion to the network layer. + See tcp_retries2 for more details. + + RFC 1122 recommends at least 3 retransmissions, which is the + default. tcp_retries2 - INTEGER - How may times to retry before killing alive TCP connection. - RFC1122 says that the limit should be longer than 100 sec. - It is too small number. Default value 15 corresponds to ~13-30min - depending on RTO. + This value influences the timeout of an alive TCP connection, + when RTO retransmissions remain unacknowledged. + Given a value of N, a hypothetical TCP connection following + exponential backoff with an initial RTO of TCP_RTO_MIN would + retransmit N times before killing the connection at the (N+1)th RTO. + + The default value of 15 yields a hypothetical timeout of 924.6 + seconds and is a lower bound for the effective timeout. + TCP will effectively time out at the first RTO which exceeds the + hypothetical timeout. + + RFC 1122 recommends at least 100 seconds for the timeout, + which corresponds to a value of at least 8. tcp_rfc1337 - BOOLEAN If set, the TCP stack behaves conforming to RFC1337. If unset, -- 1.6.3.3