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SubjectRe: [PATCH] sched: Improve readability in update_cpu_load() code
On Thu, May 15, 2008 at 08:22:15PM +0530, Srivatsa Vaddagiri wrote:
> 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 ..
>

Sorry for the noise. I must have read the previous if() condition
incorrectly.
> 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

--
Thanks and Regards
gautham


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