Re: [PATCH linux-2.6-block:master 02/05] blk: update ioscheds to use generic dispatch queue

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Jens Axboe wrote:
On Fri, Oct 21 2005, Tejun Heo wrote:

I think we're currently talking about two issues.


I think so too :)


1. Is @sort=0 case useful?

Currently all ioscheds dispatch requests in sorted order. I was afraid that sorting again might result in less efficient seek pattern although I'm not quite sure whether or how that will happen. That's why I added the @sort argument to elv_dispatch_insert(). If sorting cannot hurt in any case, we might sort unconditionally and remove @sort argument from elv_dispatch_insert().


That's what I ended up merging, elv_dispatch_sort() and it only takes q
and rq as parameters.


2. Why @force is used to turn on @sort?


Yes, that was my question :-)


The reasoning was that, when a iosched is forced dispatched, it doesn't have control over many aspects of IO scheduling, so it cannot produce good ordering of dumped requests, which actually is true for cfq. That's why @sort is turned on while force-dispatching requests.


Well that's not quite my question, it is the opposite - why would you
not want to sort?


Maybe just removing @sort argument from elv_dispatch_insert() and sorting always is the way to go?


See the merged stuff, I think so. I just don't see any reason at all to
tie 'force' and 'sort' together.


 Yeap, merged version looks fine.

--
tejun
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