From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: Integration of SCST in the mainstream Linux kernel Date: Wed, 30 Jan 2008 10:34:31 -0600 Message-ID: <1201710871.3292.22.camel@localhost.localdomain> References: <1201639331.3069.58.camel@localhost.localdomain> <20080130083239E.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from accolon.hansenpartnership.com ([76.243.235.52]:46005 "EHLO accolon.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751492AbYA3Qei (ORCPT ); Wed, 30 Jan 2008 11:34:38 -0500 In-Reply-To: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Bart Van Assche Cc: FUJITA Tomonori , rdreier@cisco.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, vst@vlnb.net, linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org On Wed, 2008-01-30 at 09:38 +0100, Bart Van Assche wrote: > On Jan 30, 2008 12:32 AM, FUJITA Tomonori wrote: > > > > iSER has parameters to limit the maximum size of RDMA (it needs to > > repeat RDMA with a poor configuration)? > > Please specify which parameters you are referring to. As you know I > had already repeated my tests with ridiculously high values for the > following iSER parameters: FirstBurstLength, MaxBurstLength and > MaxRecvDataSegmentLength (16 MB, which is more than the 1 MB block > size specified to dd). the 1Mb block size is a bit of a red herring. Unless you've specifically increased the max_sector_size and are using an sg_chain converted driver, on x86 the maximum possible transfer accumulation is 0.5MB. I certainly don't rule out that increasing the transfer size up from 0.5MB might be the way to improve STGT efficiency, since at an 1GB/s theoretical peak, that's roughly 2000 context switches per I/O; however, It doesn't look like you've done anything that will overcome the block layer limitations. James