Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934303AbZDAUYH (ORCPT ); Wed, 1 Apr 2009 16:24:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758336AbZDAUXs (ORCPT ); Wed, 1 Apr 2009 16:23:48 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:35613 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757076AbZDAUXr (ORCPT ); Wed, 1 Apr 2009 16:23:47 -0400 Subject: Re: [Iscsitarget-devel] [Scst-devel] ISCSI-SCST performance (withalso IET and STGT data) From: James Bottomley To: Ross Walker Cc: Bart Van Assche , "Ross S. W. Walker" , Vladislav Bolkhovitin , "linux-scsi@vger.kernel.org" , iSCSI Enterprise Target Developer List , "linux-kernel@vger.kernel.org" , "stgt@vger.kernel.org" , scst-devel In-Reply-To: References: <49D10256.8030307@vlnb.net> <49D11096.3070804@vlnb.net> <49D254E4.8050806@vlnb.net> Content-Type: text/plain Date: Wed, 01 Apr 2009 20:23:43 +0000 Message-Id: <1238617423.3318.82.camel@mulgrave.int.hansenpartnership.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 (2.22.3.1-1.fc9) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1625 Lines: 41 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 James -- 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/