From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Thumshirn Subject: Re: [PATCH] scsi: Allow activation of scsi-mq per-driver Date: Mon, 25 Jan 2016 11:16:14 +0100 Message-ID: <20160125101614.GD29561@c203.arch.suse.de> References: <1453470088-43959-1-git-send-email-jthumshirn@suse.de> <20160125100525.GA24369@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mx2.suse.de ([195.135.220.15]:59581 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755796AbcAYKQR (ORCPT ); Mon, 25 Jan 2016 05:16:17 -0500 Content-Disposition: inline In-Reply-To: <20160125100525.GA24369@infradead.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Christoph Hellwig Cc: James Bottomley , "Martin K. Petersen" , Hiral Patel , Suma Ramars , Brian Uchino , James Smart , Dick Kennedy , Hannes Reinecke , linux-scsi@vger.kernel.org On Mon, Jan 25, 2016 at 02:05:25AM -0800, Christoph Hellwig wrote: > On Fri, Jan 22, 2016 at 02:41:28PM +0100, Johannes Thumshirn wrote: > > Allow the activation of the scsi-mq feature on a per-driver bassis = as opposed > > to the current stack global (de)activation. > >=20 > > This allows us to have setups which can combine "slow" rotational m= edia and > > fast media on two different HBA types. >=20 > It's still the wrong thing to do. One of your co-workers has been > working on slicing for blk-mq to better support slower adapters. I know but there are no results yet. >=20 > Anything that prolongs the misery of keeping the old request code aro= und > is a bad idea. Agreed, but this patch is a "quick fix" for the problem until the nice = solution is in place. The way it currently works is unacceptable from a distribu= tion point of view. >=20 > > The following is from a host with rotational disks behind a HP SAS = Adapter and > > a fibre channel array behind a Emulex FC Adapter. The hpsa driver d= oes not > > support scsi-mq yet (and has rotational disks attached to it), but = the lpfc > > does. This patch allows an optimal combination of the scsi-mq enabl= ed lpfc > > driver and the hpsa driver which still uses a single queue scsi lay= er and thus > > can make use of IO schedulers. >=20 > And this is another reason why this is bad. There are very slow dumb > FC array arounds as well as really fast ones. And there are really s= low > SATA disks behind SAS controllers as well as really fast SSDs. >=20 > The host is simply the wrong place to decide these things. Yes, but this way the admin can _decide_ on which driver's he/she is go= ing to activate scsi-mq and on which not. Of casue this only solves the issue = if multiple drivers are involved, but still better than a global on/off sw= itch. --=20 Johannes Thumshirn Storage jthumshirn@suse.de +49 911 74053 689 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: Felix Imend=F6rffer, Jane Smithard, Graham Norton HRB 21284 (AG N=FCrnberg) Key fingerprint =3D EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850 -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html