[ltp] Aggressive Powersaving

[Karsten König]

Am Donnerstag, 25. Februar 2010 23:19:22 schrieb Pedro Ribeiro:
> 2010/2/25 Karsten König <remur@gmx.net>:
> > Am Dienstag, 9. Februar 2010 16:16:36 schrieb Henrique de Moraes Holsch=
uh:
> >> On Tue, 09 Feb 2010, Karsten König wrote:
> >> > the new kernels really brought down the power consumption and I am
> >> > interested in getting it a little bit further, on the road I don't u=
se
> >> > my DVD drive nor ExpressCard nor USB nor Firewire nor Touchpad, is
> >> > there a way to cleany cut the power to these devices/buses?
> >>
> >> Yes.  Disable them on the BIOS where possible, Linux doesn't put PCI
> >>  devices in D3 state yet as a rule, so once a driver loads and brings
> >> that device to D0 state, the device will stay powered up.  There might
> >> be exceptions.
> >
> > Hmm I disabled things like parallel port, bus disabling FireWire USB etc
> > in the BIOS is not very practical as I want to use them without having =
to
> > switch in the BIOS
> > But the PCI D3 states got me to
> > http://www.mjmwired.net/kernel/Documentation/power/pci.txt where the
> > different states and their transitions are documented, but I can't find
> > sysfs knobs for it, so I can't tell the kernel to just suspend the whole
> > USB stack unless something blocks it? I imagine this as a smaller part =
of
> > the suspend cycle, I only want parts of the system to switch off.
> 
> To enable low power PCI states in the .33 kernel, just use
> CONFIG_PCIEASPM=y
> 
> Bear in mind this is marked as EXPERIMENTAL, probably for a good reason.
> 
> That being said, I have to say that enabling it on the T400 makes no
> difference at all! I guess that is because of the BIOS setting, which
> is enabled by default (can't remember the name, but I'm pretty sure
> its related to PCI ASPM). It does not affect stability though.
> 
> However if your Thinkpad does not have this BIOS setting it might be
> worth to try it. Once the module is compiled and loaded, just use
> echo powersave > /sys/module/pcie_aspm/parameters/policy
> or
> echo performance > /sys/module/pcie_aspm/parameters/policy
> 
> Regards,
> Pedro
> 

Weee that sounds good, I'll build myself a .33 kernel when I have time on the 
weekend and see what happens, but I guess not much having the same system ;-)
http://www.lesswatts.org/projects/devices-power-management/pcie.php documents 
it as another powersaving feature which wants to do automagic what the users 
expects and might have negative side effects.


Thanks,
Karsten