lkml.org 
[lkml]   [2004]   [Oct]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: bug in sched.c:activate_task()
Date
* Chen, Kenneth W <kenneth.w.chen@intel.com> 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.


Ingo Molnar wrote on Tuesday, October 05, 2004 1:19 AM
> it is being used for multiple purposes: measuring on-CPU time, measuring
> on-runqueue time (for interactivity) and measuring off-runqueue time
> (for interactivity). It is also used to measure cache-hotness, by the
> balancing code.
>
> now, this particular update of p->timestamp:
>
> > @@ -888,7 +888,6 @@ static void activate_task(task_t *p, run
>
> > - p->timestamp = now;
>
> is important for the interactivity code that runs in schedule() - it
> wants to know how much time we spent on the runqueue without having run.
>
> but you are right that the task_hot() use of p->timestamp is incorrect
> for freshly woken up tasks - we want the balancer to be able to re-route
> tasks to another CPU, as long as the task has not hit the runqueue yet
> (which it hasnt where we consider it in the balancer).
>
> the clean solution is to separate the multiple uses of p->timestamp:
> with the patch below p->timestamp is purely used for the interactivity
> code, and p->last_ran is for the rebalancer. The patch is ontop of your
> task_hot() fix-patch. Does this work for your workload?

I will take this for a spin and report back the result.

- Ken


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:06    [W:1.239 / U:0.520 seconds]
©2003-2014 Jasper Spaans. Advertise on this site