Re: [BK PATCHES] add ata scsi driver

[Linus Torvalds (torvalds@transmeta.com)]

On Mon, 26 May 2003, Jens Axboe wrote:
> 
> I know this is a pet peeve of yours (must be, I remember you bringing it
> up at least 3 time before :), but I don't think that's necessarily true.
> It shouldn't matter _one_ bit whether you leave the request there or
> not, it's unmergeable.

It's not the merging that I worry about. It's latency and starvation.

Think of it this way: if you keep feeding a disk requests, and the disk 
always tries to do the closest one (which is a likely algorithm), you can 
easily have a situation where the disk _never_ actually schedules a 
request that is at one "end" of the platter. 

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.

> As long as the io scheduler keeps track of this (and it does!) we are
> golden.

Hmm.. Where does it keep track of request latency for requests that have 
been removed from the queue?

		Linus

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