Re: [BK PATCHES] add ata scsi driver

[Nick Piggin (piggin@cyberone.com.au)]

Linus Torvalds wrote:

> On Mon, 26 May 2003, Jens Axboe wrote:
>
> > > Think of all the fairness issues we've had in the elevator code, and 
> > > realize that the low-level disk probably implements _none_ of those 
> > > fairness algorithms.
> > I think it does, to some extent at least.
>
> I doubt they do a very good job of it. I know of bad cases, even with 
> "high-end" hardware. Sure, we can hope that it's getting better, but do we 
> want to bet on it.
>
>
> > > Hmm.. Where does it keep track of request latency for requests that have 
> > > been removed from the queue?
> > Well, it doesn't...
>
> Yeah. Which means that right now _really_ long starvation will show up as
> timeouts, while other cases will just show up as bad latency.
There is an elevator notifier which is called on request
completion in Andrew's tree (needed for AS io scheduler). This
can be used to do what you want.

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