Re: [BK PATCHES] add ata scsi driver

Nick Piggin
2003-05-26T23:46:13Z

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.