Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261210AbUDIAmI (ORCPT ); Thu, 8 Apr 2004 20:42:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261355AbUDIAmI (ORCPT ); Thu, 8 Apr 2004 20:42:08 -0400 Received: from ozlabs.org ([203.10.76.45]:21913 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S261210AbUDIAmF (ORCPT ); Thu, 8 Apr 2004 20:42:05 -0400 Date: Fri, 9 Apr 2004 10:37:37 +1000 From: Anton Blanchard To: Andy Isaacson Cc: Andrew Morton , bug-coreutils@gnu.org, linux-kernel@vger.kernel.org Subject: Re: dd PATCH: add conv=direct Message-ID: <20040409003737.GF18493@krispykreme> References: <20040406220358.GE4828@hexapodia.org> <20040406173326.0fbb9d7a.akpm@osdl.org> <20040407173116.GB2814@hexapodia.org> <20040407111841.78ae0021.akpm@osdl.org> <20040407192432.GD2814@hexapodia.org> <20040407123455.0de9ffa9.akpm@osdl.org> <20040407194727.GE2814@hexapodia.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040407194727.GE2814@hexapodia.org> User-Agent: Mutt/1.5.5.1+cvs20040105i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1295 Lines: 29 Hi, > OK, I can see that one. But it seems like a pretty small benefit to me > -- CPU utilization is already really low. Maybe not to you but it does make a big difference on our 500 disk setup. At the moment we use dd to do an initial sniff, then ext3 utils to do O_DIRECT reads/writes. With O_DIRECT read/write in dd we could use it instead. (We are basically interested in IO performance that a database would see). > Um, that sounds like a bad idea to me. It seems to me it's the kernel's > responsibility to figure out "hey, looks like a streaming read - let's > not blow out the buffer cache trying to hold 20GB on a 512M system." If > you're saying that the kernel guys have given up and the established > wisdom is now "you gotta use O_DIRECT if you don't want to throw > everything else out due to streaming data", well... I'm disappointed. When you start hitting memory bandwidth limits, O_DIRECT will help you. Sure it wont be an issue for your dd copy scenario, but I wanted to point out there are other valid uses for it. Anton - 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/