Re: SCSI dynamic power management

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Tue, 2007-11-20 at 16:36 +0100, Oliver Neukum wrote:
> Am Dienstag 20 November 2007 schrieb James Bottomley:
> > 
> > On Tue, 2007-11-20 at 16:07 +0100, Oliver Neukum wrote:
> > > Am Dienstag 20 November 2007 schrieb James Bottomley:
> > > > I don't understand why you want to do this.  Power management is a
> > > > layered issue on SCSI, divided (as always) into host, device and
> > > > transport.  The idle you're talking about is a pure device thing, so it
> > > > can be managed by the ULD (and currently is).  When a unit is stopped,
> > > 
> > > The lower layers don't know how to correctly suspend a device. sd_suspend()
> > > may know how to do it. It would also mean the LLD having to detect idleness.
> > 
> > You really mean you want to involve the transport as well, right?  So
> 
> Yes, we cannot avoid that. Some device drop their caches unless they are
> flushed.

So that would be fixed by having the ULD send a flush before START STOP
UNIT?

> > ipso facto this is more than simple idleness management.  Thus, you
> > really need to look into the full solution (host, transport and ULD).
> 
> Only detecting idleness without doing anything with that knowledge would
> be pointless :-)
> What is the right kind of sequence?

I don't really know ... I don't have a clear idea of what you're trying
to do.  I know Alan said it was something simple, but from what you're
saying it sounds like you need a full blown power management
infrastructure in all three places.

James