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    SubjectRe: Please, put 64-bit counter per task and incr.by.one each ctxt switch.
    On 2/26/08, J.C. Pizarro <jcpiza@gmail.com> wrote:
    > 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";

    Very funny.

    > 3. They don't use ++ (incr. by one per ctxt-switch).

    No they do, read schedule() already.

    > 4. I don't like the separation of voluntary and involuntary ctxt-switches,
    > and i don't understand the utility of this separation.

    Ah, that's why you don't like it.

    > 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
    > */

    6. Profit.

    As I understood the idea of CFS, all interactivity heuristics were bitbucketed,
    so you'll add them back (you won't, of course, because you can't be arsed
    to send a patch)

    So best course of action it to describe workload and setup (distro, relevant
    .config items and so on.) on which CFS behaves poorly.


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