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

[Jens Axboe <axboe@suse.de>]

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.

-- 
Jens Axboe

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