[ltp] High power consumption after suspend/resume cycle

[Theodore Tso]

On Wed, Oct 07, 2009 at 04:52:53PM +0100, Robert Tomsick wrote:
> > for i in /sys/class/scsi_host/*/link_power_management_policy; do
> >     echo min_power > $i
> > done
> > 
> > Do you have a patch that does better?
> 
> The line you posted will enable power-saving for all ports, but AFAIK it
> won't actually shut them off.
> 
> I found a patch (submitted to LKML IIRC) that actually disables all
> unused ports at init. time.  In theory it saves 0.75W -- YMMV though.

Yeah, I know about that patch.  The question is whether it actually
saves power (and if so, how much) over simply enabling ALPM by echoing
min_power > /sys/class/scs_host/*/link.  I was wondering if you had
done the measurement or not.

> I've got local copies that apply cleanly to the Debian Lenny kernel
> sources and the Ubuntu 9.04 kernel sources.  I can throw them up here if
> anyone is interested.

Can you send me the patch?  I'd be curious to do a formal test of
enabling ALPM versus forcibly disabling all of the unused.

	      	     	      		    - Ted