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

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Message-ID: <20130716211529.GQ22392@kernel.dk>
Date:	Tue, 16 Jul 2013 15:15:29 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	James Bottomley <jbottomley@...allels.com>,
	Hannes Reinecke <hare@...e.de>,
	"ksummit-2013-discuss@...ts.linuxfoundation.org" 
	<ksummit-2013-discuss@...ts.linuxfoundation.org>,
	James Smart <James.Smart@...lex.Com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kmo@...erainc.com" <kmo@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
	"scameron@...rdog.cce.hp.com" <scameron@...rdog.cce.hp.com>
Subject: Re: [Ksummit-2013-discuss] [ATTEND] scsi-mq prototype discussion

On Tue, Jul 16 2013, Nicholas A. Bellinger wrote:
> On Sat, 2013-07-13 at 06:53 +0000, James Bottomley wrote:
> > On Fri, 2013-07-12 at 12:52 +0200, Hannes Reinecke wrote:
> > > 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.
> > 
> > Lets start with discussing this on the list, please, and then see where
> > we go from there ...
> > 
> 
> Yes, the discussion is beginning to make it's way to the list.  I've
> mostly been waiting for blk-mq to get a wider review before taking the
> early scsi-mq prototype driver to a larger public audience.
> 
> Primarily, I'm now reaching out to the people most effected by existing
> scsi_request_fn() based performance limitations.  Most of them have
> abandoned existing scsi_request_fn() based logic in favor of raw block
> make_request() based drivers, and are now estimating the amount of
> effort to move to an scsi-mq based approach.
> 
> Regardless, as the prototype progresses over the next months, having a
> face-to-face discussion with the key parties in the room would be very
> helpful given the large amount of effort involved to actually make this
> type of generational shift in SCSI actually happen.

There's a certain amount of overlap with the aio/O_DIRECT work as well.
But if it's not a general session, could always be a BOF or something.

I'll second the argument that most technical topics probably DO belong
in a topic related workshop. But that leaves us with basically only
process related topics at KS, I don't think it hurts to have a bit of
tech meat on the bone too. At least I personally miss that part of KS
from years gone by.

-- 
Jens Axboe

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