Here's patches for 2.4 & 2.5 to use PAL_HALT_LIGHT in cpu_idle.
This helps to reduce CPU temp a little on boxes with firmware that
takes advantage of this lower power state.  I've tried this on a
rx2600 (2x900MHz McKinley) and an i2000 (fw 117) and it shows some
benefit.  On McKinley systems, only the very latest PAL from Intel
actually reduces power consumption in the halt_light state.  For HP
rx2600/zx6000/zx2000, this means you need to be running firmware 1.82.

  Rohit Seth, at Intel, has run some benchmarks with this kind of
modification and found the effects of enabling halt_light to fall
within the noise of mosts tests.  I replaced pal_halt(1) in safe_halt
with pal_halt_light() since halt_light is required to be implemented,
but pal_halt(1) is an optional halt state.  I'd be interested to hear
of any measurements anyone does using this, where it works/fails, and
if any benchmarks/applications are impacted.