From: john stultz <johnstul@us.ibm.com>

The patch tries to resolve issues caused by running the TSC based lost
tick compensation code on CPUs that change frequency (speedstep, etc).

Should the CPU be in slow mode when calibrate_tsc() executes, the kernel
will assume we have so many cycles per tick.  Later when the cpu speeds up,
the kernel will start noting that too many cycles have past since the last
interrupt.  Since this can occasionally happen, the lost tick compensation
code then tries to fix this by incrementing jiffies.  Thus every tick we
end up incrementing jiffies many times, causing timers to expire too
quickly and time to rush ahead.

This patch detects when there has been 100 consecutive interrupts where we
had to compensate for lost ticks.  If this occurs, we spit out a warning
and fall back to using the PIT as a time source.

I've tested this on my speedstep enabled laptop with success, and others
laptop users seeing this problem have reported it works for them.  Also to
ensure we don't fall back to the slower PIT too quickly, I tested the code
on a system I have that looses ~30 ticks about every second and it can
still manage to use the TSC as a good time source.

This solves most of the "time doubling" problems seen on laptops.
Additionally this revision has been modified to use the cleanups made in
rename-timer_A1.