Re: [patch 2.6.16-rc5-mm2] sched_cleanup-V17 - task throttling patch1 of 2

[Peter Williams]

Mike Galbraith wrote:
> On Sat, 2006-03-04 at 16:54 +1100, Con Kolivas wrote:
>
> > On Saturday 04 March 2006 16:40, Randy.Dunlap wrote:
> >
> > > On Sat, 04 Mar 2006 06:29:47 +0100 Mike Galbraith wrote:
> > >
> > > > On Sat, 2006-03-04 at 16:24 +1100, Con Kolivas wrote:
> > > >
> > > > > On Saturday 04 March 2006 16:20, Mike Galbraith wrote:
> > > > >
> > > > > > On Sat, 2006-03-04 at 13:33 +1100, Peter Williams wrote:
> > > > > >
> > > > > > > > include/linux/sched.h |    3 -
> > > > > > > > kernel/sched.c        |  136
> > > > > > > > +++++++++++++++++++++++++++++--------------------- 2 files
> > > > > > > > changed, 82 insertions(+), 57 deletions(-)
> > > > > > > >
> > > > > > > > --- linux-2.6.16-rc5-mm2/include/linux/sched.h.org	2006-03-01
> > > > > > > > 15:06:22.000000000 +0100 +++
> > > > > > > > linux-2.6.16-rc5-mm2/include/linux/sched.h	2006-03-02
> > > > > > > > 08:33:12.000000000 +0100 @@ -720,7 +720,8 @@
> > > > > > > >
> > > > > > > > 	unsigned long policy;
> > > > > > > > 	cpumask_t cpus_allowed;
> > > > > > > > -	unsigned int time_slice, first_time_slice;
> > > > > > > > +	int time_slice;
> > > > > > >
> > > > > > > Can you guarantee that int is big enough to hold a time slice in
> > > > > > > nanoseconds on all systems?  I think that you'll need more than 16
> > > > > > > bits.
> > > > > >
> > > > > > Nope, that's a big fat bug.
> > > > >
> > > > > Most ints are 32bit anyway, but even a 32 bit unsigned int overflows
> > > > > with nanoseconds at 4.2 seconds. A signed one at about half that. Our
> > > > > timeslices are never that large, but then int isn't always 32bit
> > > > > either.
> > > >
> > > > Yup.  I just didn't realize that there were 16 bit integers out there.
> > >
> > > LDD 3rd ed. doesn't know about them either.  Same for me.
> >
> > Alright I made that up, but it might not be one day :P
>
>
> Well Fudgecicles.  Now you guys have gotten me aaaaall confused.  Are
> there cpus out there (in generic linux land) that have 16 bit integers
> or not?  16 bit integers existing in a 32 bit cpu OS seems like an alien
> concept to me, but I'm not a twisted cpu designer... I'll just go with
> the flow ;-)

I'm not sure which is why I asked.  But it seems to be a convention (in 
the kernel code) to use long or unsigned long when you want to ensure at 
least 32 bits.  This may be a legacy from the days when there were 
systems with 16 bit integers but it seems (to me) to be alive and well.

Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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