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. > > > > This allows us to have setups which can combine "slow" rotational media and > > fast media on two different HBA types. > > 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. > > Anything that prolongs the misery of keeping the old request code around > 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 distribution point of view. > > > 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 does 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 enabled lpfc > > driver and the hpsa driver which still uses a single queue scsi layer and thus > > can make use of IO schedulers. > > 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 slow > SATA disks behind SAS controllers as well as really fast SSDs. > > 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 going 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 switch. -- Johannes Thumshirn Storage jthumshirn@xxxxxxx +49 911 74053 689 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850 -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
