[ltp] T61 temperature limits

[Henrique de Moraes Holschuh]

On Thu, 17 Apr 2008, Owen Heisler wrote:
> Isn't this what throttling does?

No.

> http://acpi.sourceforge.net/documentation/processor.html (legacy docs)
>  Throttling is sort of enforced power management: Even when the system is 
>  highly active, the CPU is "put to sleep" for short amounts of time.

No, it is not.  It is sort of halted part of the time, but that's
nowehere close to what deep C-states can do (C-states actually power
down parts of the CPU, T-states just mess with the clock).

> According to those two excerpts, using a T state that throttles 50%
> should force the processor(s) to spend at least half the clock cycles
> in a sleep state.

According to Intel, you are to race to C3 if you want to save power.
They know their CPU better than anyone else, so I will believe that to
be the best way to go about it on ThinkPads (which use Intel CPUs).

> But maybe it is not true, as suggested by this on thinkwiki.org.
> Maybe throttling a processor does not force it to drop to a sleep
> state.  Why not?

They're different things.  Maybe one could be tied to the other if the
CPU maker wanted to, but for Intel CPUs, they are not.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh