From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751773AbWCNIFo (ORCPT ); Tue, 14 Mar 2006 03:05:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751782AbWCNIFn (ORCPT ); Tue, 14 Mar 2006 03:05:43 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:45645 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S1751773AbWCNIFn (ORCPT ); Tue, 14 Mar 2006 03:05:43 -0500 Date: Tue, 14 Mar 2006 09:05:27 +0100 From: Jens Axboe To: Lee Revell Cc: Mike Galbraith , Andrew Morton , ck@vds.kolivas.org, linux-kernel@vger.kernel.org Subject: Re: [ck] Re: [PATCH] mm: Implement swap prefetching tweaks Message-ID: <20060314080527.GC4419@suse.de> References: <200603102054.20077.kernel@kolivas.org> <200603111650.23727.kernel@kolivas.org> <1142056851.7819.54.camel@homer> <200603111824.06274.kernel@kolivas.org> <1142063500.7605.13.camel@homer> <1142139283.25358.68.camel@mindpipe> <1142318403.4583.14.camel@homer> <1142319048.13256.103.camel@mindpipe> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1142319048.13256.103.camel@mindpipe> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 14 2006, Lee Revell wrote: > On Tue, 2006-03-14 at 07:40 +0100, Mike Galbraith wrote: > > On Sat, 2006-03-11 at 23:54 -0500, Lee Revell wrote: > > > On Sat, 2006-03-11 at 08:51 +0100, Mike Galbraith wrote: > > > > There used to be a pages in flight 'restrictor plate' in there that > > > > would have probably helped this situation at least a little. But in > > > > any case, it sounds like you'll have to find a way to submit the IO in > > > > itty bitty synchronous pieces. > > > > > > echo 64 > /sys/block/hd*/queue/max_sectors_kb > > > > > > There is basically a straight linear relation between whatever you set > > > this to and the maximum scheduling latency you see. It was developed to > > > solve the exact problem you are describing. > > > > > > > > Is it possible that you mean pci latency? I'm unable to measure any > > scheduling latency > 5ms while pushing IO for all my little Barracuda > > disk is worth. > > It's only a big problem if LBA48 is in use which allows 32MB of IO to be > in flight at once, this depends on the size of the drive. > > What does that value default to? Not quite true. Even if lba48 is active on the drive, we don't allow more than 1MB per request. And nit picking a little, lba48 doesn't always depend on the size of the drive, some drives smaller than 2^28 sectors also feature lba48 support. -- Jens Axboe