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

[Ric Wheeler]

On 07/17/2013 12:52 AM, James Bottomley wrote:
> On Tue, 2013-07-16 at 15:15 -0600, Jens Axboe wrote:
> > 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.
> 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

Ric


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