Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933747Ab1ESRo0 (ORCPT ); Thu, 19 May 2011 13:44:26 -0400 Received: from quartz.orcorp.ca ([139.142.54.143]:43583 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933666Ab1ESRoZ (ORCPT ); Thu, 19 May 2011 13:44:25 -0400 Date: Thu, 19 May 2011 11:44:20 -0600 From: Jason Gunthorpe To: Bart Van Assche Cc: "Nicholas A. Bellinger" , linux-kernel , linux-scsi , linux-rmda , Roland Dreier , Vu Pham , David Dillow , James Bottomley Subject: Re: [RFC] ib_srpt: initial .40-rc1 drivers/infiniband/ulp/srpt merge Message-ID: <20110519174420.GD12525@obsidianresearch.com> References: <1305682604-21383-1-git-send-email-nab@linux-iscsi.org> <20110518170556.GB2595@obsidianresearch.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-Broken-Reverse-DNS: no host name found for IP address 10.0.0.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1379 Lines: 28 On Thu, May 19, 2011 at 07:29:21PM +0200, Bart Van Assche wrote: > Regarding APM: the Linux kernel already has multipath support and > duplicate functionality is in general not welcomed. So you will have > to come up with a very good reason before APM support in ib_srp or > ib_srpt would be considered for acceptance. APM is a feature of IB's tranport layerthat provides disruption free lossless failover to a backup network path completely transparently to the application (eg SRP in this case). This plays a similar role in the IB stack to the realtime spanning tree protocol that ethernet uses, or the multipath IP routing that is already in the net stack. I don't see it duplicating SCSI multipath at all. On very large IB networks (eg > 1000 switches) the rate of link failures is high enough that taking an application level recovery on hundreds of nodes due to a link failure is troublesome. If ib_srpt is implemented properly it may already support APM because APM is supported by the IB CM that it relies on to setup connections, and any SRP client could already request APM functionality during connection setup. Jason -- 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/