Messages in this thread | | | Date | Tue, 11 Jul 2006 19:36:05 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] Consolidate the request merging |
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On Tue, Jul 11 2006, Nick Piggin wrote: > Jens Axboe wrote: > >Hi, > > > >Right now, every IO scheduler implements its own backmerging (except for > >noop, which does no merging). That results in duplicated code for > >essentially the same operation, which is never a good thing. This patch > >moves the backmerging out of the io schedulers and into the elevator > >core. We save 1.6kb of text and as a bonus get backmerging for noop as > >well. Win-win! > > > >Notes: > > > >- I dropped the "move hot entries to front" logic. It's never been > > proven good, and some research indicates that it's a bad idea. I doubt > > it matters in real life, so lets just cut that away. > > > >- Next it might be a good idea to move the rb sorting into the elevator > > core as well. We could save some more kernel text, but more > > importantly it gets us one step closer to dropping deadline_rq from > > the deadline scheduler. > > Seems like a good idea. I don't think this could be a downside for anyone > except maybe Ken Chen, if it adds any overhead to the noop scheduler. > > BTW, IMO it is a good idea for the noop scheduler to do as much merging as > possible, especially as it could be used for things like network block > devices (but more merging may actually cut down on CPU and IO bandwidth > even in the local disk case).
I agree, I actually think it's a win for noop with the cheap merging. If anyone complains, we can always make it tweakable with a sysfs parameter. Even for "intelligent" hardware, you have a command overhead per request, so it makes a lot of sense to always do merging.
-- Jens Axboe
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