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

[Tejun Heo <htejun@gmail.com>]

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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