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SubjectRe: [PATCH] sched: Improve readability in update_cpu_load() code
On Thu, May 15, 2008 at 06:34:59PM +0530, Gautham R Shenoy wrote:
> Author: Gautham R Shenoy <ego@in.ibm.com>
> Date: Thu May 15 17:55:49 2008 +0530
>
> sched: Improve readability in update_cpu_load() code
>
> Currently the cpu_load[i] is calculated as:
> this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
>
> However, since scale = 2^i, this can be simplified as:
> this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);
>
> Makes it easier to read.
> Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 2d7d8f1..e1a6985 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2921,7 +2921,7 @@ static void update_cpu_load(struct rq *this_rq)
> */
> if (new_load > old_load)
> new_load += scale-1;
> - this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
> + this_rq->cpu_load[i] = old_load + ((new_load - old_load) >> i);

This wont work when new_load < old_load ..

For ex: I tried this prog:

#include <stdio.h>

main()
{
unsigned long old_load = 100, new_load = 90, this_load, this_load1;
int i = 1, scale = 2 << i;
this_load = (old_load*(scale-1) + new_load) >> i;
this_load1 = old_load + ((new_load - old_load) >> i);

printf ("this_load = %u, this_load1 = %u \n", this_load, this_load1);
}
This is what I get:

$ ./a.out
this_load = 195, this_load1 = 2147483743
$



--
Regards,
vatsa


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