* Ingo Molnar <[email protected]> wrote:
> > Appended patch attempts to fix the process idle load balancing in
> > the presence of dynticks. cpus for which ticks are stopped will
> > sleep till the next event wakes it up. Potentially these sleeps can
> > be for large durations and during which today, there is no idle load
> > balancing being done. There was some discussion happened(last year)
> > on this topic on lkml, where two main approaches were gettting
> > debated. One is to back off the idle load balancing for bigger
> > intervals and the second is a watchdog mechanism where the busy cpu
> > will trigger the load balance on an idle cpu. Both of these
> > mechanisms have its drawbacks.
>
> nice work! I have added your patch to -rt. Btw., it needs the patch
> below to work on 64-bit.
there's another bug as well: in schedule() resched_cpu() is called with
the current runqueue held in two places, which is deadlock potential.
The easiest fix for this is to use trylock - find the patch for that.
This is a hint only anyway - and if a CPU is idle its runqueue will be
lockable. (fixing it via double-locking is easy in the first call site,
but the second one looks harder)
Ingo
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -1167,12 +1167,14 @@ static void resched_task(struct task_str
if (!tsk_is_polling(p))
smp_send_reschedule(cpu);
}
+
static void resched_cpu(int cpu)
{
struct rq *rq = cpu_rq(cpu);
- unsigned int flags;
+ unsigned long flags;
- spin_lock_irqsave(&rq->lock, flags);
+ if (!spin_trylock_irqsave(&rq->lock, flags))
+ return;
resched_task(cpu_curr(cpu));
spin_unlock_irqrestore(&rq->lock, flags);
}
-
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