Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759933AbZCXMYd (ORCPT ); Tue, 24 Mar 2009 08:24:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754558AbZCXMYX (ORCPT ); Tue, 24 Mar 2009 08:24:23 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:57879 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753805AbZCXMYW (ORCPT ); Tue, 24 Mar 2009 08:24:22 -0400 Date: Tue, 24 Mar 2009 12:23:26 +0000 From: Alan Cox To: Andrew Morton Cc: Ingo Molnar , Arjan van de Ven , Peter Zijlstra , Nick Piggin , Theodore Tso , Jens Axboe , David Rees , Jesper Krogh , Linus Torvalds , Linux Kernel Mailing List Subject: Re: Linux 2.6.29 Message-ID: <20090324122326.6be519f2@lxorguk.ukuu.org.uk> In-Reply-To: <20090324041249.1133efb6.akpm@linux-foundation.org> References: <49C87B87.4020108@krogh.cc> <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> X-Mailer: Claws Mail 3.7.0 (GTK+ 2.14.7; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2292 Lines: 46 > The proposed tweak to kjournald is a bad fix - partly because it will > elevate the priority of vast amounts of IO whose priority we don't _want_ > elevated. Its a huge improvement in practice because it both fixes the stupid stalls and smooths out the rest of the I/O traffic. I spend a lot of my time looking at what the disk driver is getting fed and its not a good mix. Even more revealing is the noop scheduler and the fact this frequently outperforms all the fancy I/O scheduling we do even on relatively dumb hardware (as well as showing how mixed up our I/O patterns currently are). > But mainly because the problem lies elsewhere - in an area of contention > between the committing and running transactions which we knowingly and > reluctantly added to fix a bug in The problem emerges about 2007 not 2002, so its not that simple. > The number of people who can be looked at to do serious ext3/JBD work is > pretty small now. Ted, Stephen and I got old and died. Jan does good work > but is spread thinly. Which is all the more reason to use a temporary fix in the meantime so the OS is usable. I think its pretty poor that for over a year those in the know who need a good performing system are having to apply out of tree trivial patches rejected on the basis that "eventually like maybe whenever perhaps we'll possibly some day you know consider fixing this, but don't hold your breath" There is a second reason to do this: If ext4 is the future then it is far better to fix this stuff in ext4 properly and leave ext3 clear of extremely invasive high risk fixes when a quick bandaid will do just fine for the remaining lifetime of fs/jbd Also not kjournald is only one of the afflicted threads - the same is true of the crypto, and of the vm writeback. Also note the other point about the disk scheduler defaults being terrible for some streaming I/O patterns and the patch for that is also stuck in bugzilla. If picking "no-op" speeds up my generic x86 box with random onboard SATA we are doing something very non-optimal -- 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/