From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sagi Grimberg Subject: Re: [LSF/MM TOPIC] iSCSI MQ adoption via MCS discussion Date: Fri, 09 Jan 2015 13:39:08 +0200 Message-ID: <54AFBDDC.1000107@dev.mellanox.co.il> References: <54AD5DDD.2090808@dev.mellanox.co.il> <54AD6563.4040603@suse.de> <54ADA777.6090801@cs.wisc.edu> <54AE36CE.8020509@acm.org> <54AE8A02.1030100@dev.mellanox.co.il> <54AE9010.5080609@acm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wg0-f45.google.com ([74.125.82.45]:44212 "EHLO mail-wg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755101AbbAILjQ (ORCPT ); Fri, 9 Jan 2015 06:39:16 -0500 Received: by mail-wg0-f45.google.com with SMTP id b13so7612401wgh.4 for ; Fri, 09 Jan 2015 03:39:14 -0800 (PST) In-Reply-To: <54AE9010.5080609@acm.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Bart Van Assche , open-iscsi@googlegroups.com, Hannes Reinecke , lsf-pc@lists.linux-foundation.org Cc: linux-scsi , target-devel , Oren Duer , Or Gerlitz On 1/8/2015 4:11 PM, Bart Van Assche wrote: > On 01/08/15 14:45, Sagi Grimberg wrote: >> Actually I started with that approach, but the independent connections >> under a single session (I-T-Nexus) violates the command ordering >> requirement. Plus, such a solution is specific to iSER... > > Hello Sagi, > > Which command ordering requirement are you referring to ? The Linux > storage stack does not guarantee that block layer or SCSI commands will > be processed in the same order as these commands have been submitted. > I was referring to the iSCSI session requirement. I initially thought of an approach to maintain multiple iSER connections under a single session but pretty soon I realized that preserving commands ordering this way is not feasible. So independent iSER connections means independent iSCSI sessions (each with a single connection). This is indeed another choice, which we are clearly debating on... I'm just wandering if we are not trying to force-fit this model. How would this model look like? We will need to define another entity to track and maintain the sessions and to allocate the scsi_host. Will that be communicated to user-space? How will error recovery look like? Sagi.