Hi all,

Thanks for all the comments, here's an updated version of the dynamic
tick patch.

I've fixed couple of things:

- Dyn-tick now supports local APIC timer. This allows longer sleep time
  inbetween ticks, over 1000 ticks compared to 54 ticks with PIT timer.
  It seems to stop timers on SMP too, but I've only briefly played with
  it on SMP.

- Fixed a stupid bug where next_timer_interrupt() was called, but
  jiffies was not substracted from the value. This caused the sleep to
  be always maximum available...

- CONFIG_HPET_TIMER is still not supported, but now the dyn-tick should
  automatically get disabled if HPET timer is detected.

- Now processor _should_ stay in idle for the duration of skipped ticks,
  as PIT and local APIC timers are disabled. I haven't verified this
  though.

I haven't fixes some things, such as the separation of the idle loop
into it's own module, the generic part does not really do much
anyting, etc.

Please note that this patch alone probably does not produce any
considerable power savings. More work is needed in the PM area to take
advantage of the savings. Some examples of the work needed are:

- There's lots of polling timers being used in Linux, such as in the 
  keyboard driver, that keeps the ticks skipped very short. Many of
  these timers could be improved.

- There's currently no way to specify what kind of idle to use based on
  the estimated length of the sleep. For example, if the system supports
  ACPI C3 state, it should be possible to automatically enter C3 if the
  skippable jiffies are long enough. I believe the current ACPI idle
  loop bases the promotion/demotion to the number of idle loops run in
  certain time, which does not work when skipping ticks.

Please also note that this patch does not solve the high-resolution
timers issues. This patch is intended to be a minimal patch to expose
and improve PM related issues.

The main difference between dyn-tick patch compared to the high-res VST
patch is that dyn-tick uses the next_timer_interrupt() function, and 
does not require the high-res timers patch to be installed. In the long
run the dyn-tick and VST patches will probably merge. But meanwhile, 
PM related work can be done that benefits both patches.

Again, comments and testing is appreciated! If having problems, please
provide output of dmesg | grep -i "time\|tick\|apic".

Regards,

Tony