Power-Mgt (Was: Re: cvs commit: src/sys/i386/cpufreq est.c )

[Robert Watson]

On Mon, 17 Mar 2008, Poul-Henning Kamp wrote:

> In message <47DED21C.4070108 at FreeBSD.org>, Kris Kennaway writes:
>
>> I think this is a great idea, but one of the big problems is probably going 
>> to be dealing with hardware quirks.  e.g. we can't even enable powerd by 
>> default because e.g. acpi_throttle hangs on some systems.  It might be 
>> tricky to get power management to the stage where it works for everyone and 
>> can be done automatically.
>
> I'd expect that this will improve over time, just like all other 
> technologies from ISA to PCI bus implementations did.
>
> But yes, it will take time & effort, but given the current 
> cleantech/greentech buzz, I think we'd better get moving.

I know we've talked about this, but I'll mention it for the benefits of the 
mailing list: one of the things that makes performance an "easy" target is 
that there are easy-to-gather metrics.  Those metrics may require knowledge of 
statistics and a lifetime of experience to interpret correctly, but they are 
still numbers that are easily generated and compared.  To drive work in power 
management, we would benefit from having similarly accessible metrics.  Are 
there any decent documents describing how to do power use measurement, and are 
there any (relatively) accessible tools for doing it with?  For example, on 
notebooks, can we sample an ACPI value before/after a benchmark, or do we 
really need to hook something up to the power supply in order to get a useful 
number?

Robert N M Watson
Computer Laboratory
University of Cambridge