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    SubjectRe: Please, put 64-bit counter per task and incr.by.one each ctxt switch.
    On 2008/2/25, Andrew Morton <akpm@linux-foundation.org> wrote:
    > On Sun, 24 Feb 2008 14:12:47 +0100 "J.C. Pizarro" <jcpiza@gmail.com> wrote:
    >
    > > It's statistic, yes, but it's a very important parameter for the CPU-scheduler.
    > > The CPU-scheduler will know the number of context switches of each task
    > > before of to take a blind decision into infinitum!.
    >
    >
    > We already have these:
    >
    > unsigned long nvcsw, nivcsw; /* context switch counts */
    >
    > in the task_struct.

    1. They use "unsigned long" instead "unsigned long long".
    2. They use "= 0;" instead of "= 0ULL";
    3. They don't use ++ (incr. by one per ctxt-switch).
    4. I don't like the separation of voluntary and involuntary ctxt-switches,
    and i don't understand the utility of this separation.

    The tsk->nvcsw & tsk->nivcsw mean different to i had proposed.

    It's simple, when calling to function kernel/sched.c:context_switch(..)
    to do ++, but they don't do it.

    I propose you
    1. unsigned long long tsk->ncsw = 0ULL; and tsk->ncsw++;
    2. unsigned long long tsk->last_registered_ncsw = tsk->ncsw; when it's polling.
    3. long tsk->vcsw = ( tsk->ncsw - tsk->last_registered_ncsw ) / ( t2 - t1 )
    /* velocity of task (ctxt-switches per second), (t1 != t2 in seconds
    for no zerodiv)
    4. long tsk->last_registered_vcsw = tsk->vcsw;
    5. long tsk->normalized_vcsw =
    (1 - alpha)*tsk->last_registered_vcsw + alpha*tsk->vcsw; /* 0<alpha<1 */

    Sincerely yours ;)


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