Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757134AbZCYSeU (ORCPT ); Wed, 25 Mar 2009 14:34:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751591AbZCYSeA (ORCPT ); Wed, 25 Mar 2009 14:34:00 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:39991 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007AbZCYSeA (ORCPT ); Wed, 25 Mar 2009 14:34:00 -0400 Date: Wed, 25 Mar 2009 11:26:57 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: David Rees cc: Theodore Tso , Jan Kara , Andrew Morton , Ingo Molnar , Alan Cox , Arjan van de Ven , Peter Zijlstra , Nick Piggin , Jens Axboe , Jesper Krogh , Linux Kernel Mailing List Subject: Re: Linux 2.6.29 In-Reply-To: Message-ID: References: <72dbd3150903232346g5af126d7sb5ad4949a7b5041f@mail.gmail.com> <20090324091545.758d00f5@lxorguk.ukuu.org.uk> <20090324093245.GA22483@elte.hu> <20090324101011.6555a0b9@lxorguk.ukuu.org.uk> <20090324103111.GA26691@elte.hu> <20090324041249.1133efb6.akpm@linux-foundation.org> <20090325123744.GK23439@duck.suse.cz> <20090325150041.GM32307@mit.edu> <72dbd3150903251109x75aa5d8ke8277247c2f292f9@mail.gmail.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1129 Lines: 27 On Wed, 25 Mar 2009, Linus Torvalds wrote: > > Even a suck-ass laptop drive can write streaming data fast enough that > people don't care. The problem is invariably that writes from different > sources (much of it being metadata) interact and cause seeking. Actually, not just writes. The IO priority thing is almost certainly that _reads_ (which get higher priority by default due to being synchronous) get interspersed with the writes, and then even if you _could_ be having streaming writes, what you actually end up with is lots of seeking. Again, good SSD's don't care. Disks do. It doesn't matter if you have a FC disk array that can eat 300MB/s when streaming - once you start seeking, that 300MB/s goes down like a rock. Battery-protected write caches will help - but not a whole lot when streaming more data than they have RAM. Basic queuing theory. Linus -- 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/