hard disk power down (was: Re: PowerTOP tool released; time to fix the wasted laptop power on fedora?)

[Richard Hughes]

On Sun, 2007-05-13 at 19:24 +0200, Thorsten Leemhuis wrote:
> On 13.05.2007 19:06, Arjan van de Ven wrote:
> > On Sun, 2007-05-13 at 23:52 +1000, David Timms wrote:
> >> Arjan van de Ven wrote:
> >>> some of you already know that I've been working on getting Linux (and
> >>> Fedora) to be a lot better about power usage on laptops by avoiding
> >>> spurious wakeups and context switches and such (look at the "wakeup" bug
> >>> in fedora bugzilla ;).
> >> ...
> >> Would this tool help one in tracing the cause of disk accesses in an 
> >> otherwise inactive/idle notebook. It seems to be about every 3 seconds 
> >> or so that the hard disk LED lights. This must make it impossible for 
> >> the hard drive to get powered down - and save power.
> > I've gotten this request a few times now; I'll be looking into this for
> > version 2.0; I'd think it would be possible with blktrace but I need to
> > look into the details (don't want this tracing to spoil any other
> > measurements ;)

(cheers for the cc)

> Just wondering: does Fedora spin down the hard disk by default? It
> doesn't afaics and it's not easily user-configurable either afaik.

It doesn't - you have to be very careful with the amount of power it
takes to spin-up a drive (often significant) compared to the amount of
time it's spun down.

The amount of disk accesses is indeed horrific in a modern distro, and
the drive doesn't usually spin down for long, even with laptop-mode
flushing. This is bad.

> Gnome-power-manager sounds like the proper place to control if the hard
> disk gets powered down; but well, seem Richard got burned when he tried
> it last time:

Heh, burned is one word. :-)

Unless we keep the disk from spinning up, my patch isn't actually that
effective. I am however using a similar patch to HAL on my media center
embedded PC, where I'm only running a pretty stripped system, and spin
the disks down mostly for noise, not power saving.

My view still is that this is a valid patch to HAL, and I would be quite
happy to do the action automatically in g-p-m. I'm not sure we need UI -
we can probably just profile the mean time that the disk is idle and
work out if it is worth powering down.

Ideas welcome.

> See http://lists.freedesktop.org/archives/hal/2005-October/003538.html
> and quoting from http://live.gnome.org/GnomePowerManager/FAQ :
> ----
> GNOME Power Manager doesn't spin down my hard-drive!
> 
> After numerous debates, the consensus was that is was not a good idea to
> add this functionality to HAL. It's was decided user-configurable
> powermanagement was not really required when modern hard disks have
> really intelligent powermanagment.

(I wrote this after numerous conversations with dannyk) 

True about the intelligent pm, although I still think we can make big
savings if we do this carefully.

> ...You can't set powermanagement for exteral USB
> harddisks, because you can't send the needed commands over the USB link
> to the disk.

Can we still do this using libata?

> So maybe this is not worth the trouble?

I think it is - we are trimming easy stuff (like cpufreq and brightness)
and I think we need to start looking at the drive spindown with a new
vigour.

Richard.

(g-p-m dude)