On Mon, Oct 13, 2003 at 09:37:15AM -0700, Bill Studenmund wrote:
> > 
> > It's not always appropriate to do things as fast as we can, in parallel.
> > I have several boxes with SCSI disks where auto spin up of the disks are
> > disabled, and I rely on the sequential prove to have them spin up sequentially.
> > If they all spin up at the same time there could be power problems.
> > 
> > Note that I don't think your proposal would cause problems here (the
> > spin up happens at attach time, and attach are still sequencial here,
> > if I understood it properly), just a general point.
> 
> The heavy-iron I've seen that has to worry about power addressed it 
> directly. I know the Convex disk racks we had at NASA had three power 
> strips, and had delayed power-up on them. That way everything started up 
> fine, and no OS intervention needed.

not everyone can afford power devices that can do this properly :(

> > I'm not sure I follow you here. For devices with several deepth of
> > subdevices (e.g atabus -> atapibus -> sd), we can't probe sd before
> > atapibus is attached (because we need the atapibus's kernel thread for
> > example).
> 
> We do whatever is needed to make the probe happen. The tree-like structure 
> was more a reference to USB.
> 
> Do we really have an atabibus thread _and_ an atabus thread covering the
> same sd? That seems rather wasteful.

The atabus thread covers everything attached to the atabus (that is,
wd and low level requests from atapibus).
The atapibus thread covers what's attached to the atapibus, for high-level
functionalities.

I've been thinking of ways to have a single thread handle boths. The problem
is that we can have atapibus without atabus, or atabus without atapibus (and
atapibus can attach to something else than atabus).

--
Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
     NetBSD: 24 ans d'experience feront toujours la difference
--