* Darren Hart <[email protected]> wrote:
> Thanks for the updated patch! It wouldn't quite build (proc_misc.c
> still referenced the old rt_overload_* variables, fixup patch attached
> removing those print statements). [...]
doh, forgot to send those changes ...
> [...] I have it running on a 4 way opteron box running prio-preempt
> in a timed while loop, exiting only on failure. It's been running
> fine for several minutes - usually fails in under a mintue. We'll see
> how it's doing in the morning :-)
meanwhile i've released -rt3 with the fix (and the procfs change)
included.
i slept on it meanwhile, and i think the safest would be to also do the
attached patch ontop of -rt3. This makes the 'kick other CPUs' logic
totally unconditional - so whatever happens the wakeup code will notice
if an RT task is in trouble finding the right CPU. Under -rt3 we'd only
run into this branch if we stayed on the same CPU - but there can be
cases when we have your scenario even in precisely such a case. It's
rare but possible.
Ingo
Index: linux-rt.q/kernel/sched.c
===================================================================
--- linux-rt.q.orig/kernel/sched.c
+++ linux-rt.q/kernel/sched.c
@@ -1588,38 +1588,37 @@ out_set_cpu:
this_cpu = smp_processor_id();
cpu = task_cpu(p);
- } else {
+ }
+ /*
+ * If a newly woken up RT task cannot preempt the
+ * current (RT) task (on a target runqueue) then try
+ * to find another CPU it can preempt:
+ */
+ if (rt_task(p) && !TASK_PREEMPTS_CURR(p, rq)) {
+ this_rq = cpu_rq(this_cpu);
/*
- * If a newly woken up RT task cannot preempt the
- * current (RT) task (on a target runqueue) then try
- * to find another CPU it can preempt:
+ * Special-case: the task on this CPU can be
+ * preempted. In that case there's no need to
+ * trigger reschedules on other CPUs, we can
+ * mark the current task for reschedule.
+ *
+ * (Note that it's safe to access this_rq without
+ * extra locking in this particular case, because
+ * we are on the current CPU.)
*/
- if (rt_task(p) && !TASK_PREEMPTS_CURR(p, rq)) {
- this_rq = cpu_rq(this_cpu);
+ if (TASK_PREEMPTS_CURR(p, this_rq))
+ set_tsk_need_resched(this_rq->curr);
+ else
/*
- * Special-case: the task on this CPU can be
- * preempted. In that case there's no need to
- * trigger reschedules on other CPUs, we can
- * mark the current task for reschedule.
- *
- * (Note that it's safe to access this_rq without
- * extra locking in this particular case, because
- * we are on the current CPU.)
+ * Neither the intended target runqueue
+ * nor the current CPU can take this task.
+ * Trigger a reschedule on all other CPUs
+ * nevertheless, maybe one of them can take
+ * this task:
*/
- if (TASK_PREEMPTS_CURR(p, this_rq))
- set_tsk_need_resched(this_rq->curr);
- else
- /*
- * Neither the intended target runqueue
- * nor the current CPU can take this task.
- * Trigger a reschedule on all other CPUs
- * nevertheless, maybe one of them can take
- * this task:
- */
- smp_send_reschedule_allbutself();
+ smp_send_reschedule_allbutself();
- schedstat_inc(this_rq, rto_wakeup);
- }
+ schedstat_inc(this_rq, rto_wakeup);
}
out_activate:
-
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