From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753580AbcA3IdA (ORCPT ); Sat, 30 Jan 2016 03:33:00 -0500 Received: from mx2.suse.de ([195.135.220.15]:46308 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752062AbcA3Ic7 (ORCPT ); Sat, 30 Jan 2016 03:32:59 -0500 Subject: Re: [PATCH v2] dm pref-path: provides preferred path load balance policy To: Benjamin Marzinski , "Nalla, Ravikanth" References: <1453469502-15606-1-git-send-email-ravikanth.nalla@hpe.com> <56A231C8.90602@suse.de> <20160122165932.GA28761@redhat.com> <49D617FA63152941907AADE32CF072F12FD72905@G4W3202.americas.hpqcorp.net> <20160129175059.GB24960@octiron.msp.redhat.com> Cc: Mike Snitzer , "dm-devel@redhat.com" , "linux-kernel@vger.kernel.org" , "corbet@lwn.net" From: Hannes Reinecke Message-ID: <56AC7535.2090401@suse.de> Date: Sat, 30 Jan 2016 09:32:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: <20160129175059.GB24960@octiron.msp.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/29/2016 06:50 PM, Benjamin Marzinski wrote: > On Fri, Jan 29, 2016 at 02:10:52PM +0000, Nalla, Ravikanth wrote: >> Hi Mike, Hannes, Ben >>> This seems like a problem that has already been solved with path groups. >>> If the path(s) in your preferred path group are there, multipath will >>> use them. If not, then it will use your less preferred path(s), and >>> load balance across them > how ever you choose with the path_selectors. >>> >>> I admit that we don't have a path prioritizer that does a good job of >>> allowing users to manually pick a specific path to prefer. But it seems >>> to me that there is > >where we should be solving the issue. >>> >> Yes as mentioned , it appears that we will be able to achieve the same >> result using the above multipath{...} configuration. However as you >> mentioned I felt that it is not that user friendly in specify the path >> to prefer. So when you mentioned about solving the problem there, could >> you please clarify on what you had in mind and is there anything specific >> from our implementation that can be used there ? >> > > There are two changes that I'm working on. > > 1. I'm adding an option for the alua prioritizer so that setting the > ALUA TPG Preferred Bit will cause the alau prioritizer to put that path > in a group by itself (with the highest priority). Currently if the > preferred bit is set for an active/optimized path, and there are other > active/optimized paths, they are all grouped together, and there is no > way to change that. So, for people with ALUA enabled hardware, they can > just enable the option, and set the Preferred Bit. > Hmm? I was under the distinct impression that it's exactly the other way round; at least in my code I have this: switch(aas) { case AAS_OPTIMIZED: rc = 50; break; case AAS_NON_OPTIMIZED: rc = 10; break; case AAS_LBA_DEPENDENT: rc = 5; break; case AAS_STANDBY: rc = 1; break; default: rc = 0; } if (priopath && aas != AAS_OPTIMIZED) rc += 80; ie any path with the 'prio' bit set will be getting a differen priority than those without. Consequently they'll be grouped into different priority groups. I'd be surprised if your code is different, but what do I know ... > 2. For people that need to be able to control the exact priority, I'm > redoing the weighted handler to allow better ways to specify the paths > in a presistent manner. It won't be as simple as the alua method, but > it will be actually usable, unlike it's current state. > That, however, is greatly appreciated :-) Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)