From: Vladislav Bolkhovitin Subject: Re: Slow file transfer speeds with CFQ IO scheduler in some cases Date: Tue, 17 Feb 2009 22:01:13 +0300 Message-ID: <499B0979.8050006@vlnb.net> References: <20081112190227.GS26778@kernel.dk> <1226566313.199910.29888@de> <492BDAA9.4090405@vlnb.net> <20081125113048.GB16422@localhost> <492BE47B.3010802@vlnb.net> <20081125114908.GA16545@localhost> <492BE97A.3050606@vlnb.net> <492BEAE8.9050809@vlnb.net> <20081125121534.GA16778@localhost> <492EDCFB.7080302@vlnb.net> <20081128004830.GA8874@localhost> <49946BE6.1040005@vlnb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: Jeff Moyer , "Vitaly V. Bursov" , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org To: Wu Fengguang , Jens Axboe Return-path: Received: from moutng.kundenserver.de ([212.227.126.186]:60408 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752328AbZBQTBN (ORCPT ); Tue, 17 Feb 2009 14:01:13 -0500 In-Reply-To: <49946BE6.1040005-d+Crzxg7Rs0@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: Vladislav Bolkhovitin, on 02/12/2009 09:35 PM wrote: > Additional interesting observation is how badly simultaneous read IO > streams are handled, if they aren't grouped in the corresponding IO > contexts. In test 3 the result was as low as 4(!)MB/s. Wu, Jens, do you > have any explanation on this? Why the inner tracks have so big preference? I realized, there is another explanation: access becomes about to be completely random. I checked and it is true. Here is a sample "iostat -x 3" output on the server: avg-cpu: %user %nice %system %iowait %steal %idle 0.00 0.00 0.57 26.62 0.00 72.81 Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util sda 710.00 0.00 47.33 0.00 6058.67 0.00 128.00 0.12 2.59 2.51 11.87 sdb 710.00 0.00 47.33 0.00 6058.67 0.00 128.00 3.99 84.34 21.13 100.00 sdc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 sdc1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 sdc2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 md0 0.00 0.00 1514.67 0.00 12117.33 0.00 8.00 0.00 0.00 0.00 0.00 dm-0 0.00 0.00 757.33 0.00 6058.67 0.00 8.00 32.87 43.41 1.32 100.00 dm-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 dm-2 0.00 0.00 757.33 0.00 6058.67 0.00 8.00 32.79 43.33 1.32 100.00 Thanks, Vlad