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    SubjectRe: [ANNOUNCE] sched: schedtop utility
    Hi Peter,

    On Thu, Jun 19, 2008 at 12:27:14PM +0200, Peter Zijlstra wrote:
    > On Thu, 2008-06-05 at 10:50 +0530, Ankita Garg wrote:
    >
    > > Thanks Peter for the explanation...
    > >
    > > I agree with the above and that is the reason why I did not see weird
    > > values with cpu_time. But, run_delay still would suffer skews as the end
    > > points for delta could be taken on different cpus due to migration (more
    > > so on RT kernel due to the push-pull operations). With the below patch,
    > > I could not reproduce the issue I had seen earlier. After every dequeue,
    > > we take the delta and start wait measurements from zero when moved to a
    > > different rq.
    >
    > OK, so task delay delay accounting is broken because it doesn't take
    > migration into account.
    >
    > What you've done is make it symmetric wrt enqueue, and account it like
    >
    > cpu0 cpu1
    >
    > enqueue
    > <wait-d1>
    > dequeue
    > enqueue
    > <wait-d2>
    > run
    >
    > Where you add both d1 and d2 to the run_delay,.. right?
    >

    Thanks for reviewing the patch. The above is exactly what I have done.

    > This seems like a good fix, however it looks like the patch will break
    > compilation in !CONFIG_SCHEDSTATS && !CONFIG_TASK_DELAY_ACCT, of it
    > failing to provide a stub for sched_info_dequeue() in that case.
    >

    Fixed. Pl. find the new patch below.

    Signed-off-by: Ankita Garg <ankita@in.ibm.com>

    Index: linux-2.6.24.4/kernel/sched.c
    ===================================================================
    --- linux-2.6.24.4.orig/kernel/sched.c 2008-06-05 13:31:53.000000000 +0530
    +++ linux-2.6.24.4/kernel/sched.c 2008-07-01 14:03:58.000000000 +0530
    @@ -948,6 +948,7 @@

    static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
    {
    + sched_info_dequeued(p);
    p->sched_class->dequeue_task(rq, p, sleep);
    p->se.on_rq = 0;
    }
    Index: linux-2.6.24.4/kernel/sched_stats.h
    ===================================================================
    --- linux-2.6.24.4.orig/kernel/sched_stats.h 2008-06-05 13:31:53.000000000 +0530
    +++ linux-2.6.24.4/kernel/sched_stats.h 2008-07-01 14:23:32.000000000 +0530
    @@ -113,6 +113,13 @@
    if (rq)
    rq->rq_sched_info.cpu_time += delta;
    }
    +
    +static inline void
    +rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
    +{
    + if (rq)
    + rq->rq_sched_info.run_delay += delta;
    +}
    # define schedstat_inc(rq, field) do { (rq)->field++; } while (0)
    # define schedstat_add(rq, field, amt) do { (rq)->field += (amt); } while (0)
    # define schedstat_set(var, val) do { var = (val); } while (0)
    @@ -121,6 +128,9 @@
    rq_sched_info_arrive(struct rq *rq, unsigned long long delta)
    {}
    static inline void
    +rq_sched_info_dequeued(struct rq *rq, unsigned long long delta)
    +{}
    +static inline void
    rq_sched_info_depart(struct rq *rq, unsigned long long delta)
    {}
    # define schedstat_inc(rq, field) do { } while (0)
    @@ -129,6 +139,11 @@
    #endif

    #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
    +static inline void sched_info_reset_dequeued(struct task_struct *t)
    +{
    + t->sched_info.last_queued = 0;
    +}
    +
    /*
    * Called when a process is dequeued from the active array and given
    * the cpu. We should note that with the exception of interactive
    @@ -138,15 +153,22 @@
    * active queue, thus delaying tasks in the expired queue from running;
    * see scheduler_tick()).
    *
    - * This function is only called from sched_info_arrive(), rather than
    - * dequeue_task(). Even though a task may be queued and dequeued multiple
    - * times as it is shuffled about, we're really interested in knowing how
    - * long it was from the *first* time it was queued to the time that it
    - * finally hit a cpu.
    + * Though we are interested in knowing how long it was from the *first* time a
    + * task was queued to the time that it finally hit a cpu, we call this routine
    + * from dequeue_task() to account for possible rq->clock skew across cpus. The
    + * delta taken on each cpu would annul the skew.
    */
    static inline void sched_info_dequeued(struct task_struct *t)
    {
    - t->sched_info.last_queued = 0;
    + unsigned long long now = task_rq(t)->clock, delta = 0;
    +
    + if(unlikely(sched_info_on()))
    + if(t->sched_info.last_queued)
    + delta = now - t->sched_info.last_queued;
    + sched_info_reset_dequeued(t);
    + t->sched_info.run_delay += delta;
    +
    + rq_sched_info_dequeued(task_rq(t), delta);
    }

    /*
    @@ -160,7 +182,7 @@

    if (t->sched_info.last_queued)
    delta = now - t->sched_info.last_queued;
    - sched_info_dequeued(t);
    + sched_info_reset_dequeued(t);
    t->sched_info.run_delay += delta;
    t->sched_info.last_arrival = now;
    t->sched_info.pcount++;
    @@ -231,7 +253,9 @@
    __sched_info_switch(prev, next);
    }
    #else
    -#define sched_info_queued(t) do { } while (0)
    -#define sched_info_switch(t, next) do { } while (0)
    +#define sched_info_queued(t) do { } while (0)
    +#define sched_info_reset_dequeued(t) do { } while (0)
    +#define sched_info_dequeued(t) do { } while (0)
    +#define sched_info_switch(t, next) do { } while (0)
    #endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */

    --
    Regards,
    Ankita Garg (ankita@in.ibm.com)
    Linux Technology Center
    IBM India Systems & Technology Labs,
    Bangalore, India


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