Messages in this thread | | | Date | Mon, 2 Jun 2014 14:57:30 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH RFC - TAKE TWO - 00/12] New version of the BFQ I/O Scheduler |
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On Mon, Jun 02 2014, Tejun Heo wrote: > Hello, > > On Mon, Jun 02, 2014 at 11:46:36AM -0600, Jens Axboe wrote: > > But blk-mq will potentially drive anything, so it might not be out of > > the question with a more expensive scheduling variant, if it makes any > > sense to do of course. At least until there's no more rotating stuff out > > there :-). But it's not a priority at all to me yet. As long as we have > > coexisting IO paths, it'd be trivial to select the needed one based on > > the device characteristics. > > Hmmm... yeah, moving rotating devices over to blk-mq doesn't really > seem beneficial to me. I think there are fundamental behavioral > differences for rotating rusts and newer solid state devices to share > single code path for things like scheduling and selecting the > appropriate path depending on the actual devices sounds like a much > better plan even in the long term.
It's not so much about it being more beneficial to run in blk-mq, as it is about not having two code paths. But yes, we're likely going to maintain that code for a long time, so it's not going anywhere anytime soon.
And for scsi-mq, it's already opt-in, though on a per-host basis. Doing finer granularity than that is going to be difficult, unless we let legacy-block and blk-mq share a tag map (though that would not be too hard).
-- Jens Axboe
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