Subject: Re: [patch 06/10] 40x decrementer fixes

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sat, 04 Aug 2007 12:28:11 +1000

On Fri, 2007-08-03 at 20:47 +0400, Sergei Shtylyov wrote:
> Josh Boyer wrote:
> 
> > Allow generic_calibrate_decr to work for 40x platforms.  Given that the hardware
> > behavior is identical, this also changes the set_dec function to reload the PIT
> > on 40x to match the behavior 44x currently has.
> 
>     Why bother doing this?! This will only warrant you imprecise decrementer 
> interrupts while it should be interrupting at the precise period currently (if 
> you load PIT once)...

Because that's what the kernel timekeeping code expects ? The reference
time is the timebase and it doesn't drift.

The DEC/PIT is commonly used to trigger any timing, such as what is done
for lost interrupts on some platforms. Also, with dynticks, we'll most
certainly want variable reload values as well.

So I'm very happy to have Josh change the code that way. It makes things
more consistent accross the board and removes confusion.

Ben.