Re: Linux-Kernel Archive: No 100 HZ timer !

[David Schleef <ds@schleef.org>]

On Thu, Apr 12, 2001 at 09:04:28PM -0700, Andre Hedrick wrote:
> On Thu, 12 Apr 2001, george anzinger wrote:
> 
> > Actually we could do the same thing they did for errno, i.e.
> > 
> > #define jiffies get_jiffies()
> > extern unsigned get_jiffies(void);
> 
> > No, not really.  HZ still defines the units of jiffies and most all the
> > timing is still related to it.  Its just that interrupts are only "set
> > up" when a "real" time event is due.
> 
> Great HZ always defines units of jiffies, but that is worthless if there
> is not a ruleset that tells me a value to divide by to return it to a
> specific quantity of time.

It makes more sense to start migrating drivers to macros such as
msec_to_jiffies(), msec_to_whatever_add_timer_wants(), etc.  (Names
changed to protect the innocent.)  And leave HZ approximately the
way it is, because that's what the code expects.

A good transition is for add_timer() to be defined as

  #define add_timer(a) add_timer_ns(a*1000000000/HZ)

although this causes problems with timers over 4 seconds.  As much
as I like nanoseconds, it's probably overkill here, since one should
be requesting absolute time if it's specified in nanoseconds.




dave...