Message-ID: <440A0A31.6000404@bigpond.net.au>
Date: Sun, 05 Mar 2006 08:44:17 +1100
From: Peter Williams <pwil3058@bigpond.net.au>
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To: Mike Galbraith <efault@gmx.de>
CC: Con Kolivas <kernel@kolivas.org>, "Randy.Dunlap" <rdunlap@xenotime.net>,
       linux-kernel@vger.kernel.org, mingo@elte.hu, nickpiggin@yahoo.com.au,
       kenneth.w.chen@intel.com, akpm@osdl.org
Subject: Re: [patch 2.6.16-rc5-mm2]  sched_cleanup-V17 - task throttling	patch
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References: <1140183903.14128.77.camel@homer>	 <1141450187.7703.40.camel@homer>	 <20060303214002.f36ce0b4.rdunlap@xenotime.net>	 <200603041654.59480.kernel@kolivas.org> <1141455048.9482.13.camel@homer>
In-Reply-To: <1141455048.9482.13.camel@homer>
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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@bigpond.net.au

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