Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751833AbXA0OxQ (ORCPT ); Sat, 27 Jan 2007 09:53:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751836AbXA0OxP (ORCPT ); Sat, 27 Jan 2007 09:53:15 -0500 Received: from tmailer.gwdg.de ([134.76.10.23]:57215 "EHLO tmailer.gwdg.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751833AbXA0OxP (ORCPT ); Sat, 27 Jan 2007 09:53:15 -0500 Date: Sat, 27 Jan 2007 15:51:42 +0100 (MET) From: Jan Engelhardt To: vandrove@vc.cvut.cz cc: Pierre Ossman , LKML Subject: Re: ncpfs and TCP vs UDP In-Reply-To: <1169846450.45ba70b2698c2@imap.vc.cvut.cz> Message-ID: References: <45BA2437.4000803@drzeus.cx> <1169846450.45ba70b2698c2@imap.vc.cvut.cz> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Spam-Report: Content analysis: 0.0 points, 6.0 required _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1661 Lines: 38 On Jan 26 2007 22:20, vandrove@vc.cvut.cz wrote: >Quoting Pierre Ossman : > >TCP is definitely preferred. There are couple of reasons why you should >prefer TCP: > >(1) There is server configuration option to disable NCP/UDP. You cannot >disable NCP/TCP that easily. > >(2) TCP (NCP over TCP) retransmits only missing data, and it can ask for >retransmit much sooner as it knows what link latency is. NCP/UDP can only ask >for complete packet retransmission, and it has no good idea what's link >latency because there is no ACK from server when it receives request - you can >only resend after usual link latency + time for process request, so you'll >wait longer for retransmit, and on retransmit you need to send again complete >request (which can be 64KB of data if you use 64KB buffer size...) > >(3) To avoid problems with retransmits ncpfs uses default buffer size 60KB for >TCP (SOCK_STREAM), while 1KB for UDP/IPX (it must be multiple of sector size, >so using 1.4KB is not an option). So if you read 1 page, you get 1 >request/reply when using TCP, but 4 requests/replies in UDP/IPX. And as all >this is fully synchronous, and for today's link latency is dominating factor, >it will take 4 times longer... [and (4)] Well, probably the same reason as NFS over UDP is discouraged. See nfs(5) section WARNINGS (in short: IP fragment ID can wrap quite fast on Gigabit) -`J' -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/