Re: Over/Underclocking motherboards on the fly without rebooting
- From: Paul <nospam@xxxxxxxxxx>
- Date: Sun, 13 Sep 2009 16:22:49 -0400
Will wrote:
I haven't attempted to do any research on the deeper sleep states,
Don't know what you mean by "deeper sleep states". I never mentioned sleep. I just need to underclock it most of the time then have the ability to overclock it quickly when I need more power.
See the section here "C2E and C4E States and Intel VRD 11.1".
When a processor is idle, it doesn't need to do anything until the
next clock tick interrupt occurs. It is possible to put the processor
in a sort of "micro sleep" state, when that happens. So the processor
is not sleeping, like when you go to Start:Turn Off Computer and
select Standby. It is sleeping for some number of milliseconds.
Apparently, one possible option, is to drop Vcore for those
milliseconds, invalidating the cache, and keeping leakage current
pretty low. So these C states, are variations on Halt, Stop Grant
(bus disconnect) and the like. They're improvements in the ways
that subsystems on the processor can be shut down, for milliseconds
at a time.
http://www.bit-tech.net/hardware/motherboards/2008/08/20/gigabyte-ga-ep34-ds3r/12
In a processor design, if you do some of that stuff too much, the
result can be slow real time response, when the processor load is
cyclic. Anandtech has noticed a problem with video playback
on AMD processors, when Cool N' Quiet is enabled. So there
is a balance that needs to be struck, when enabling features that
put the processor into a millisecond sleep condition.
Anandtech had an article a while back, where they tried to get one
of those C states working on a laptop, and there was some issue
with Windows and the USB driver, preventing the processor
from using less power. And in that bit-tech article, there is
similar evidence, that one of the magic states is not working
right. Just the act of attempting to monitor the state, by
having a process active looking for it, can raise the utilization
level of the processor high enough, that the ACPI code doesn't
bother to use the lowest power states.
I did a quick look, for an article that explains all the C-states
in detail. But I didn't find anything I liked. There must be an article
around somewhere, that does a good job of explaining them. I doubt
the ACPI spec would have that kind of detail, as you wouldn't expect
processor technology advancements to be embedded in the spec.
For all the concentration on the processor, there are plenty of
other things in the computer that could use a look as well. Some of my
older hard drives might be 12 watts, while a new SSD could be around 2 watts.
If you used cheesy built-in motherboard graphics, instead of a video card,
that might save 25 watts. So there are other things you could look at.
Paul
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