Francois Marier wrote:
Package: acpi-support
Version: 0.103-5
Severity: wishlist
Tags: patch
Here are two scripts from https://wiki.ubuntu.com/ReducedPowerUsage which I
have added
to /etc/acpi/ac.d and /etc/acpi/battery.d to try to reduce my power usage while
on battery.
They have to do with tweaking the Linux virtual memory manager and setting the
wireless
adapter (Intel ipw-3945 in my case) power-saving mode.
Hi Francois,
Thank you for contributing. At this point I think I will not include
these additions, for several reasons:
* They are not clearly intended to make things "work" (which is what the
package is for, basically).
* Making things "work better" (which is what these patches intend to do)
usually involves some trade-offs, and those may require conscious
decisions by the user, or at least configuration settings which you can
turn off. So it's a bit more work than simply including these scripts.
* Regarding trade-offs: the scripts may break things. For instance, if
the power saving mode of iwl3945 wouldn't have drawbacks, it would
probably have been on by default in the hardware. It wouldn't even have
been a choice. :-) Probably, the power saving mode for iwl3945 will
reduce the effective range of wireless, which is not acceptable if you
use your laptop on battery in your garden. People will have a very hard
time tracing such a loss of connectivity back to acpi-support if they
didn't consciously choose to turn this power saving feature on.
* I must say I don't really agree with the VM tweaks. For instance, if
this means what I think it does:
echo 0 > /proc/sys/vm/dirty_expire_centisecs
echo 0 > /proc/sys/vm/dirty_writeback_centisecs
then it will either turn off writeback, or it will make the laptop write
everything back to the hard drive immediately. The former situation is
very dangerous (power loss = lose everything!), while the latter option
is asking for both performance problems and you can forget about ALPM
power savings (see http://www.lesswatts.org/tips/disks.php) and spinning
down the disk when it is idle.
* The VM settings are also tweaked by laptop-mode-tools, which many
laptop users install as well. I make an explicit point of not
interfering with what laptop-mode-tools handles. And arguably, the
combinations of settings applied used by laptop-mode-tools save more
power, because they actually make disk I/O more "chunky", allowing the
hardware to go into power saving mode in between batches.
* Laptop mode tools also allows you to enable wireless power saving, and
does it better: it supports this for several other types of wireless
interfaces as well. So if you want it, it's already there, no
programming required.
Cheers,
Bart
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