Re: [PATCH 2/2] sched: fix cpupri priocount

[Peter Zijlstra]

On Wed, 2008-06-04 at 15:04 -0400, Gregory Haskins wrote:
> A rounding error was pointed out by Peter Zijlstra which would result
> in the structure holding priorities to be off by one.
> 
> Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
> 
>  kernel/sched_cpupri.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/sched_cpupri.h b/kernel/sched_cpupri.h
> index 16d29b9..817c55c 100644
> --- a/kernel/sched_cpupri.h
> +++ b/kernel/sched_cpupri.h
> @@ -4,7 +4,7 @@
>  #include <linux/sched.h>
>  
>  #define CPUPRI_NR_PRIORITIES 2+MAX_RT_PRIO
> -#define CPUPRI_NR_PRI_WORDS CPUPRI_NR_PRIORITIES/BITS_PER_LONG
> +#define CPUPRI_NR_PRI_WORDS (CPUPRI_NR_PRIORITIES + BITS_PER_LONG/2)/BITS_PER_LONG

(33 + 16) / 32 = 49 / 32 = 1

So its still wrong ;-)

Please use DECLARE_BITMAP and or BITS_TO_LONGS to avoid these issues.

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