One of these things (CONFIG_HZ) is not like the others..

[Russell King - ARM Linux]

On Mon, Jan 21, 2013 at 02:36:13PM -0800, John Stultz wrote:
> Well, Russell brought up a case that doesn't handle this. If a system  
> *can't* do HZ=100, but can do HZ=200.
>
> Though there are hacks, of course, that might get around this (skip  
> every other interrupt at 200HZ).

Note: in the early days of EBSA110 support, yes, we did that, so that
we could have HZ=100 everywhere.  _However_ it sufficiently peturbed
NTP that it basically was unable to slew the clock in any sane manner.
I never got to the bottom of why that was, and when USER_HZ was
decoupled from the kernel HZ, it allowed the problem to be fixed, and
the kernel code to become a _lot_ cleaner.