Re: bug in sched.c:activate_task()

[Ingo Molnar]

On Mon, 4 Oct 2004, Chen, Kenneth W wrote:

> Update p->timestamp to "now" in activate_task() doesn't look right to me
> at all.  p->timestamp records last time it was running on a cpu.  
> activate_task shouldn't update that variable when it queues a task on
> the runqueue.

correct, we are overriding it in schedule():

        if (likely(prev != next)) {
                next->timestamp = now;
                rq->nr_switches++;

the line your patch removes is a remnant of an earlier logic when we
timestamped tasks when they touched the runqueue. (vs. timestamping when
they actually run on a CPU.) So the patch looks good to me. Andrew, please
apply.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

        Ingo


> 
> This bug (and combined with others) triggers improper load balancing.
> 
> Patch against linux-2.6.9-rc3.  Didn't diff it against 2.6.9-rc3-mm2
> because mm tree has so many change in sched.c.
> 
> Signed-off-by: Ken Chen <kenneth.w.chen@xxxxxxxxx>
> 
> 
> --- linux-2.6.9-rc3/kernel/sched.c.orig	2004-10-04 19:11:21.000000000 -0700
> +++ linux-2.6.9-rc3/kernel/sched.c	2004-10-04 19:11:35.000000000 -0700
> @@ -888,7 +888,6 @@ static void activate_task(task_t *p, run
>  			p->activated = 1;
>  		}
>  	}
> -	p->timestamp = now;
> 
>  	__activate_task(p, rq);
>  }
> 
> 
> -
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