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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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