Re: [DO NOT APPLY] sd take advantage of rotation speed

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, Jun 25 2008, Matthew Wilcox wrote:
> On Wed, Jun 25, 2008 at 06:57:59PM +0200, Jens Axboe wrote:
> > Precisely, merging and fairness is a big part of it. Plus, doing this in
> > sd is just a blatant layer violation.
> 
> I'm fine with tweaking the elevators to know about low-latency seeks.
> But please stop describing it as "a blatant layering violation".
> It's nothing of the sort.  It's setting a default at a point where we
> find out the information which would guide us.

Uhm, but it IS "a blatant layering violation", it's doing things from
the wrong side up :-)

> I haven't looked into doing this in udev yet; I've got caught up in
> another project.  In any case, it seems like there's no role for udev
> any more, so I'll probably not spend any more time on this unless there's
> some need.

I don't think udev is a particularly good idea either. My plan was to
introduce device profiles for the queue, but it is probably a bad idea
to over-engineer this. So I'll keep it simple, stick to a 'zero cost
seek' flag instead and allow drivers to signal that. libata/ide needs to
check the ID page word to detect SSD drives as well, so they need a few
lines of change too.

I'll just stick the block bit in the 2.6.27 pending queue and let the
other patches go through Jeff/James/Bart.

-- 
Jens Axboe