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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