Messages in this thread Patch in this message | | | Date | Thu, 14 Dec 2006 00:13:16 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC] Patch: dynticks: idle load balancing |
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* Ingo Molnar <mingo@elte.hu> 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); } - 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/
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