Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934352AbZDBHjV (ORCPT ); Thu, 2 Apr 2009 03:39:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758486AbZDBHjE (ORCPT ); Thu, 2 Apr 2009 03:39:04 -0400 Received: from moutng.kundenserver.de ([212.227.126.188]:58890 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756500AbZDBHjB (ORCPT ); Thu, 2 Apr 2009 03:39:01 -0400 Message-ID: <49D46B8B.5000708@vlnb.net> Date: Thu, 02 Apr 2009 11:38:51 +0400 From: Vladislav Bolkhovitin User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: James Bottomley CC: Ross Walker , "linux-scsi@vger.kernel.org" , iSCSI Enterprise Target Developer List , "linux-kernel@vger.kernel.org" , "Ross S. W. Walker" , scst-devel , "stgt@vger.kernel.org" , Bart Van Assche Subject: Re: [Scst-devel] [Iscsitarget-devel] ISCSI-SCST performance (with also IET and STGT data) References: <49D10256.8030307@vlnb.net> <49D11096.3070804@vlnb.net> <49D254E4.8050806@vlnb.net> <1238617423.3318.82.camel@mulgrave.int.hansenpartnership.com> In-Reply-To: <1238617423.3318.82.camel@mulgrave.int.hansenpartnership.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V01U2FsdGVkX19BzbBzI/HYzjyA2qwdEQvkGOG1tUJnlgh5em2 +3XbPz0nBuXfl833aIuhERJKOXIPVPfEI+6w74q93H45fKKR9N urtrnWnbZiF/iujCTtN/g== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2110 Lines: 48 James Bottomley, on 04/02/2009 12:23 AM wrote: > On Wed, 2009-04-01 at 08:20 -0400, Ross Walker wrote: >> On Apr 1, 2009, at 2:29 AM, Bart Van Assche >> wrote: >> >>> On Tue, Mar 31, 2009 at 8:43 PM, Ross S. W. Walker >>> wrote: >>>> IET just needs to fix how it does it workload with CFQ which >>>> somehow SCST has overcome. Of course SCST tweaks the Linux kernel to >>>> gain some extra speed. >>> I'm not familiar with the implementation details of CFQ, but I know >>> that one of the changes between SCST 1.0.0 and SCST 1.0.1 is that the >>> default number of kernel threads of the scst_vdisk kernel module has >>> been increased to 5. Could this explain the performance difference >>> between SCST and IET for FILEIO and BLOCKIO ? >> Thank for the update. IET has used 8 threads per target for ages now, >> I don't think it is that. >> >> It may be how the I/O threads are forked in SCST that causes them to >> be in the same I/O context with each other. >> >> I'm pretty sure implementing a version of the patch that was used for >> the dump command (found on the LKML) will fix this. >> >> But thanks goes to Vlad for pointing this dificiency out so we can fix >> it to help make IET even better. > > SCST explicitly fiddles with the io context to get this to happen. It > has a hack to block to export alloc_io_context: > > http://marc.info/?t=122893564800003 Correct, although I wouldn't call it "fiddle", rather "grouping" ;) But that's not the only reason for good performance. Particularly, it can't explain Bart's tmpfs results from the previous message, where the majority of I/O done to/from RAM without any I/O scheduler involved. (Or does I/O scheduler also involved with tmpfs?) Bart has 4GB RAM, if I remember correctly, i.e. the test data set was 25% of RAM. Thanks, Vlad -- 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/