From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ronald Moesbergen Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev Date: Fri, 10 Jul 2009 08:32:26 +0200 Message-ID: References: <4A3CD62B.1020407@vlnb.net> <4A4DE3C1.5080307@vlnb.net> <4A51DC0A.10302@vlnb.net> <4A5238EC.1070505@vlnb.net> <4A5395FD.2040507@vlnb.net> <4A5493A8.2000806@vlnb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: fengguang.wu@intel.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, Alan.Brunelle@hp.com, hifumi.hisashi@oss.ntt.co.jp, linux-fsdevel@vger.kernel.org, jens.axboe@oracle.com, randy.dunlap@oracle.com, Bart Van Assche To: Vladislav Bolkhovitin Return-path: Received: from fg-out-1718.google.com ([72.14.220.153]:37620 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751138AbZGJGc2 (ORCPT ); Fri, 10 Jul 2009 02:32:28 -0400 In-Reply-To: <4A5493A8.2000806@vlnb.net> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 2009/7/8 Vladislav Bolkhovitin : > Ronald Moesbergen, on 07/08/2009 12:49 PM wrote: >> >> 2009/7/7 Vladislav Bolkhovitin : >>> >>> Ronald Moesbergen, on 07/07/2009 10:49 AM wrote: >>>>>>> >>>>>>> I think, most likely, there was some confusion between the tested and >>>>>>> patched versions of the kernel or you forgot to apply the io_context >>>>>>> patch. >>>>>>> Please recheck. >>>>>> >>>>>> The tests above were definitely done right, I just rechecked the >>>>>> patches, and I do see an average increase of about 10MB/s over an >>>>>> unpatched kernel. But overall the performance is still pretty bad. >>>>> >>>>> Have you rebuild and reinstall SCST after patching kernel? >>>> >>>> Yes I have. And the warning about missing io_context patches wasn't >>>> there during the compilation. >>> >>> Can you update to the latest trunk/ and send me the kernel logs from the >>> kernel's boot after one dd with any block size you like >128K and the >>> transfer rate the dd reported, please? >>> >> >> I think I just reproduced the 'wrong' result: >> >> dd if=/dev/sdc of=/dev/null bs=512K count=2000 >> 2000+0 records in >> 2000+0 records out >> 1048576000 bytes (1.0 GB) copied, 12.1291 s, 86.5 MB/s >> >> This happens when I do a 'dd' on the device with a mounted filesystem. >> The filesystem mount causes some of the blocks on the device to be >> cached and therefore the results are wrong. This was not the case in >> all the blockdev-perftest run's I did (the filesystem was never >> mounted). > > Why do you think the file system (which one, BTW?) has any additional > caching if you did "echo 3 > /proc/sys/vm/drop_caches" before the tests? All > block devices and file systems use the same cache facilities. I didn't drop the caches because I just restarted both machines and thought that would be enough. But because of the mounted filesystem the results were invalid. (The filesystem is OCFS2, but that doesn't matter). > I've also long ago noticed that reading data from block devices is slower > than from files from mounted on those block devices file systems. Can > anybody explain it? > > Looks like this is strangeness #2 which we uncovered in our tests (the first > one was earlier in this thread why the context RA doesn't work with > cooperative I/O threads as good as it should). > > Can you rerun the same 11 tests over a file on the file system, please? I'll see what I can do. Just te be sure: you want me to run blockdev-perftest on a file on the OCFS2 filesystem which is mounted on the client over iScsi, right? Ronald.