CPUs with variable speed clocks ?

[Ben Scott]

On 11/3/06, Paul Lussier <p.lussier at comcast.net> wrote:
> Has anyone here encountered such a beast?

  Sure.  They've been standard issue on laptops for years.  The Intel
brand name is "SpeedStep"; for AMD it is "PowerNow.  A Google for
"Linux SpeedStep PowerNow" appears to be promising.

  Modern processors may also include the capability to "turn off" or
"slow down" parts that aren't being used right as much.  For example,
if nothing is hitting the FPU on a Pentium 4, that happens.  I believe
that is all "automatic" at the hardware level, though.

  Further back, Linux has long had a feature where, if there are no
processes ready to run (i.e., all blocked on I/O), the scheduler
issues a "HLT" instruction to the CPU, which in turn knows to reduce
its operations.  I discovered that my old 300 MHz AMD K6 ran
measurably cooler with Linux than Windows 98!

-- Ben