[Discuss] AMD FX-8120 update

[mark at buttery.org (Shirley Márquez Dúlcey)]

On 3/6/2012 9:16 AM, Bill Bogstad wrote:
> On Tue, Mar 6, 2012 at 8:44 AM, Chuck Anderson<cra at wpi.edu>  wrote:
>> On Tue, Mar 06, 2012 at 04:27:07AM -0500, Shirley M?rquez D?lcey 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.