linux-kernel - Re: [Ksummit-2013-discuss] [ATTEND] scsi-mq prototype discussion

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Date:	Fri, 12 Jul 2013 12:52:37 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	Greg KH <greg@...ah.com>,
	ksummit-2013-discuss@...ts.linuxfoundation.org,
	Jens Axboe <axboe@...nel.dk>,
	James Smart <James.Smart@...lex.Com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <jbottomley@...allels.com>,
	Andrew Vasquez <andrew.vasquez@...gic.com>, kmo@...erainc.com,
	target-devel <target-devel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
	scameron@...rdog.cce.hp.com
Subject: Re: [Ksummit-2013-discuss] [ATTEND] scsi-mq prototype discussion

On 07/12/2013 03:33 AM, Nicholas A. Bellinger wrote:
> On Thu, 2013-07-11 at 18:02 -0700, Greg KH wrote:
>> On Thu, Jul 11, 2013 at 05:23:32PM -0700, Nicholas A. Bellinger wrote:
>>> Drilling down the work items ahead of a real mainline push is high on
>>> priority list for discussion.
>>>
>>> The parties to be included in such a discussion are:
>>>
>>>   - Jens Axboe (blk-mq author)
>>>   - James Bottomley (scsi maintainer)
>>>   - Christoph Hellwig (scsi)
>>>   - Martin Petersen (scsi)
>>>   - Tejun Heo (block + libata)
>>>   - Hannes Reinecke (scsi error recovery)
>>>   - Kent Overstreet (block, per-cpu ida)
>>>   - Stephen Cameron (scsi-over-pcie driver)
>>>   - Andrew Vasquez (qla2xxx LLD)
>>>   - James Smart (lpfc LLD)
>>
>> Isn't this something that should have been discussed at the storage
>> mini-summit a few months ago?
> 
> The scsi-mq prototype, along with blk-mq (in it's current form) did not
> exist a few short months ago.  ;)
> 
>>  It seems very specific to one subsystem to be a kernel summit topic,
>> don't you think?
> 
> It's no more subsystem specific than half of the other proposals so far,
> and given it's reach across multiple subsystems (block, scsi, target),
> and the amount of off-list interest on the topic, I think it would make
> a good candidate for discussion.
> 
And it'll open up new approaches which previously were dismissed,
like re-implementing multipathing on top of scsi-mq, giving us the
single scsi device like other UNIX systems.

Also I do think there's quite some synergy to be had, as with blk-mq
we could nail each queue to a processor, which would eliminate the
need for locking.
Which could be useful for other subsystems, too.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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