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Re: sched_find_first_bit()

On Sun, 2003-12-07 at 13:01, Shinpei Kato wrote:

> I see! Can I ask one more thing. Look at following codes.
> 
> ++++
> #define BITMAP_SIZE ((((MAX_PRIO+1+7)/8)+sizeof(long)-1)/sizeof(long))
> 
> struct prio_array {
> 	int nr_active;
> 	unsigned long bitmap[BITMAP_SIZE];
> 	struct list_head queue[MAX_PRIO];
> };
> ++++
> 
> The default MAX_PRIO is defined 140 and if we assume the size of long is
> 32 bits, BITMAP_SIZE comes to be ((((140+1+7)/8)+4-1)/4)) = 5. So a
> range of b[0] to b[4] is related to MAX_PRIO, isn't it?

Yup.  What BITMAP_SIZE does is find the smallest array of longs that
would fit MAX_PRIO bits.  That size is 5 on 32-bit machines, since
(5*32=160) > (MAX_PRIO=140) > (4*32=128).

And that b[0]..b[4] is exactly what sched_find_first_bit() checks.  So
b[0] is the first 32-bits, corresponding to priority 0..31, etc.

> > Looking at the source helps a lot.
> 
> Certainly.
> 
> Thank you for your sharing your time to explain details.

No problem.

Good luck.

	Rob Love


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