Re: disk head scheduling
Arvind Sankar (arvinds@mit.edu)
Thu, 18 Mar 1999 17:13:16 -0500
On Thu, Mar 18, 1999 at 10:52:44PM +0100, Ingo Molnar wrote:
>
> On Thu, 18 Mar 1999, Arvind Sankar wrote:
>
> > > > Another point is that IN_ORDER seems to be called only for two requests
> > > > on the same device, so no idea why it compares the device numbers.
> > >
> > > no, all requests (for all devices) are in a single 'queue'. (Per-major
> > > device queues is candidate 2.3 feature, it's really simple)
> >
> > oh. I realized that it was at least per-major, but it's global, huh?
>
> the sorting (the elevator algorithm) is per-device. The queue is
> technically one queue, but thats just an implementation matter. (and of
> course it matters in the case when we hit the queue length limit)
ah. But it is per major-device linking. It would be nice to have per physical
device linking, then we could do a two-way elevator algorithm.
-- arvind
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