[laptop-mode] [Fwd: Re: Laptop-mode-tools does not refresh when ac is unplugged (ubuntu jaunty LPIA)]

[Bart Samwel]

Hi Andrea,

Andrea Cimitan wrote:
> We have the same laptop :-)

Good choice. :-)

> Of course the problem is in the ubuntu pa ackage, it doesn't seem to
> handle the acpi events.
> I will file a bug asking for upgrading their packages.

Actually, they do this by design. I hate it personally, but they chose
to do it like this at one point and they haven't undone it yet.

Basically, in Debian it's:

  acpid -> laptop-mode-tools

and in Ubuntu it's:

  acpid ->
     acpi-support ->
       [if enabled in /etc/default/acpi-support] laptop-mode-tools

But it never hurts to remind them once again in a bug report that this
is not how it should be, and that laptop-mode-tools has very fine acpid
bindings itself. :-)

> OT: Since you have a netbook (hyperthreading instead multicore) does
> /sys/devices/system/cpu/sched_smt_power_savings save power?
> laptop-mode-tools supports only multicore settings.

Nope, that doesn't save power. The multicore settings are possibly going
to be removed from a future version as well, since they don't save power
in a typical laptop situation. The way I understand it, you need a true
multi-socket system (two physical processor packages in separate
sockets) with multiple cores per socket in order to have a benefit.
Apparently it works like this, if you have a system with cores like this:

SOCKET 1
	CORE A
	CORE B

SOCKET 2
	CORE C
	CORE D

And you have two processes that can run, it then schedules the processes
on cores A and B or C and D, but not on A and C, A and D, B and C or B
and D. It always tries to put everyting on just one socket.

The sched_smt_power_savings works similarly, but replace "core" by
"hyperthreading virtual processor" in the preceding discussion. The
smallest situation where this can save power is if you have:

SOCKET 1
	PHYSICAL CORE A
		VIRTUAL PROCESSOR 1
		VIRTUAL PROCESSOR 2
	PHYSICAL CORE B
		VIRTUAL PROCESSOR 3
		VIRTUAL PROCESSOR 4

In this case, it will prefer to schedule processes to run on virtual
processor 1+2 or 3+4, so that the other physical core on the CPU can be
shut down in the mean time. Again, that only works if you have two
physical cores, which the Atom processor doesn't have. So no savings there!

Cheers,
Bart