Re: SATA powersave patches

[Pavel Machek <pavel@ucw.cz>]

Hi!

> >Thanks... I got it to work (on 2 the old tree, I was not able to
> >forward-port it), but power savings were not too big (~0.1W, maybe).
> >
> >I'm getting huge (~1W) savings by powering down SATA controller, as in
> >ahci_pci_device_suspend().
> 
> Yeah, it only turns off SATA PHY, so it doesn't result in huge saving. 
> IIRC, it was somewhere around 5 percent on my notebook w/ static 
> linksave mode (turning PHY off on empty port).  But link powersaving 
> introduces virtually no recognizable delay, so it's nice to have.

Yes, any powersavings without cost are a good idea. 

> Can you check if there is any difference between [D/H]IPS and static? 
> ICH6M on my notebook can't do DIPS/HIPS, so I couldn't compare them 
> against static.

What is D/HIPS? I could not find anything relevant..

> >It would be great to be able to power SATA
> >controller down, then power it back up when it is needed... I tried
> >following hack, but could not get it to work. Any ideas?
> 
> 1. One way to do it would be by dynamic power management.  It would be 
> nice to have wake-up mechanism at the block layer.  Idle timer can run 
> in the block layer or it can be implemented in the userland.
> 
> ATM, this implies that the attached devices are powered down too 
> (spindown).  As spinning up takes quite some time, we can implement 

For now, powering down controller when disks are spinned down would be
very nice first step.

When I forced disk to be spinned down (with power/state file)
controller actually survived power down/power up... unfortunately with
so long delay (~30 sec) that it is not usable in practice.

> So, I think option #1 is the way to go - implementing leveled dynamic 
> power management infrastructure and adding support in the block layer. 
> What do you think?

Would be nice :-).
								Pavel

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