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

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Date:	Mon, 22 Jul 2013 10:34:15 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Ric Wheeler <rwheeler@...hat.com>
Cc:	James Bottomley <jbottomley@...allels.com>,
	"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>,
	"scameron@...rdog.cce.hp.com" <scameron@...rdog.cce.hp.com>,
	"kmo@...erainc.com" <kmo@...erainc.com>,
	target-devel <target-devel@...r.kernel.org>,
	Hannes Reinecke <hare@...e.de>, Tejun Heo <tj@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Andrew Vasquez <andrew.vasquez@...gic.com>
Subject: Re: [Ksummit-2013-discuss] [ATTEND] scsi-mq prototype discussion

On Fri, Jul 19 2013, Ric Wheeler wrote:
> 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.
> >Heh well, given that most of the block mq discussions at LSF have been
> >you saying you really should get around to cleaning up and posting the
> >code, you'll understand my wanting to see that happen first ...
> >
> >I suppose we could try to run a storage workshop within KS, but I think
> >most of the mini summit slots have already gone.  There's also plumbers
> >if all slots are gone (I would say that, being biased and on the
> >programme committee) Ric is running the storage and Filesystems MC
> >
> >http://www.linuxplumbersconf.org/2013/ocw/events/LPC2013/tracks/159
> >
> >James
> >
> 
> And we still are looking for suggested topics - it would be great to have
> the multi-queue work at plumbers.
> 
> You can post a proposal for it (or other topics) here:
> 
> http://www.linuxplumbersconf.org/2013/ocw/events/LPC2013/proposals

FWIW, I can't make Plumbers this year, unfortunately.

-- 
Jens Axboe

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