On 3/6/2012 9:16 AM, Bill Bogstad wrote:
On Tue, Mar 6, 2012 at 8:44 AM, Chuck Anderson<c...@wpi.edu> wrote:
On Tue, Mar 06, 2012 at 04:27:07AM -0500, Shirley Márquez Dúlcey wrote:
The fact that the correct strategy for maximum performance may be
different from the best power management strategy is likely to require
new OS capabilities (changing the scheduling strategy based on power
management settings). If I have four things running on a desktop system
I'd likely prefer to spread them among all four modules for maximum
speed, but on a laptop I might prefer to put them on only two modules
and take the performance hit to get the power reduction of shutting off
the other two modules.
I'm not so sure you would gain anything by shutting off modules. It
was found with CPU frequency governors that slowing down a processor
actually used MORE power, because it took longer to complete running
tasks. It is better to have the CPU always run as fast as it can
while there are running tasks, and then halt the processor when it is
truley idle.
Depends on the kind of task. Some tasks have time limits (viewing a
video) rather then fixed computational goals.
And there are things like gaming where the program will grab all the
computational resources it can use to achieve a higher frame rate. But
games are typically single-threaded or use a small number of threads so
they won't use all eight cores; they will take 100% of one core plus
possibly some time on additional cores. One example I'm familiar with is
Second Life; the bulk of the viewer runs as one thread, but texture
downloading and decoding runs as multiple additional threads, sound and
music playback are another thread, and voice chat (if enabled) is a
separate process. All of this adds up to the program being able to
completely saturate two cores and make partial inroads on a third,
especially if voice chat is on.
A laptop user running on batteries might well choose to accept a 10-20%
lower frame rate in exchange for longer battery life, and for the same
reason might choose not to enable Turbo Core.
Viewing a video is not CPU-intense on most modern systems, as modern
GPUs have decoding acceleration. Power management of the GPU is another
story! It will get even more complicated with AMD's APUs, which are
outside the current discussion - but they'll be right in it in the
future when AMD releases APUs based on the architecture used in Bulldozer.
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