Re: [PATCH] sched/deadline: Use IPI to trigger DL task push migration instead of pulling

[Wanpeng Li <wanpeng.li@linux.intel.com>]

On Mon, Mar 30, 2015 at 09:41:40AM -0400, Steven Rostedt wrote:
>On Mon, 30 Mar 2015 07:07:10 +0800
>Wanpeng Li <wanpeng.li@linux.intel.com> wrote:
>
>> +static int find_next_push_cpu(struct rq *rq)
>> +{
>> +	struct rq *next_rq;
>> +	int cpu;
>> +
>> +	while (1) {
>> +		cpu = dlo_next_cpu(rq);
>> +		if (cpu >= nr_cpu_ids)
>> +			break;
>> +		next_rq = cpu_rq(cpu);
>> +
>> +		/* Make sure the next rq can push to this rq */
>> +		if (dl_time_before(next_rq->dl.earliest_dl.next,
>> +			rq->dl.earliest_dl.curr))
>> +			break;
>> +	}
>> +
>> +	return cpu;
>> +}
>> +
>
>Is it possible that we don't duplicate the code and that we can find a
>way to share the code between rt and dl? It's not that trivial to just
>cut and paste. If a bug is found in one, it most likely wont be ported
>to the other.
>
>The best is if we can share the code here some way. Perhaps have a
>single IPI that checks both rt and dl?

Peter, Juri, what's your ideas? ;)

Regards,
Wanpeng Li 

>
>-- Steve
>
>> +#define RT_PUSH_IPI_EXECUTING		1
>> +#define RT_PUSH_IPI_RESTART		2
>> +
>> +static void tell_cpu_to_push(struct rq *rq)
>> +{
>> +	int cpu;
>> +
>> +	if (rq->dl.push_flags & RT_PUSH_IPI_EXECUTING) {
>> +		raw_spin_lock(&rq->dl.push_lock);
>> +		/* Make sure it's still executing */
>> +		if (rq->dl.push_flags & RT_PUSH_IPI_EXECUTING) {
>> +			/*
>> +			 * Tell the IPI to restart the loop as things have
>> +			 * changed since it started.
>> +			 */
>> +			rq->dl.push_flags |= RT_PUSH_IPI_RESTART;
>> +			raw_spin_unlock(&rq->dl.push_lock);
>> +			return;
>> +		}
>> +		raw_spin_unlock(&rq->dl.push_lock);
>> +	}
>> +
>> +	/* When here, there's no IPI going around */
>> +
>> +	rq->dl.push_cpu = rq->cpu;
>> +	cpu = find_next_push_cpu(rq);
>> +	if (cpu >= nr_cpu_ids)
>> +		return;
>> +
>> +	rq->dl.push_flags = RT_PUSH_IPI_EXECUTING;
>> +
>> +	irq_work_queue_on(&rq->dl.push_work, cpu);
>> +}
>> +
>> +/* Called from hardirq context */
>> +static void try_to_push_tasks(void *arg)
>> +{
>> +	struct dl_rq *dl_rq = arg;
>> +	struct rq *rq, *src_rq;
>> +	int this_cpu;
>> +	int cpu;
>> +
>> +	this_cpu = dl_rq->push_cpu;
>> +
>> +	/* Paranoid check */
>> +	BUG_ON(this_cpu != smp_processor_id());
>> +
>> +	rq = cpu_rq(this_cpu);
>> +	src_rq = rq_of_dl_rq(dl_rq);
>> +
>> +again:
>> +	if (has_pushable_dl_tasks(rq)) {
>> +		raw_spin_lock(&rq->lock);
>> +		push_dl_task(rq);
>> +		raw_spin_unlock(&rq->lock);
>> +	}
>> +
>> +	/* Pass the IPI to the next rt overloaded queue */
>> +	raw_spin_lock(&dl_rq->push_lock);
>> +	/*
>> +	 * If the source queue changed since the IPI went out,
>> +	 * we need to restart the search from that CPU again.
>> +	 */
>> +	if (dl_rq->push_flags & RT_PUSH_IPI_RESTART) {
>> +		dl_rq->push_flags &= ~RT_PUSH_IPI_RESTART;
>> +		dl_rq->push_cpu = src_rq->cpu;
>> +	}
>> +
>> +	cpu = find_next_push_cpu(src_rq);
>> +
>> +	if (cpu >= nr_cpu_ids)
>> +		dl_rq->push_flags &= ~RT_PUSH_IPI_EXECUTING;
>> +	raw_spin_unlock(&dl_rq->push_lock);
>> +
>> +	if (cpu >= nr_cpu_ids)
>> +		return;
>> +
>> +	/*
>> +	 * It is possible that a restart caused this CPU to be
>> +	 * chosen again. Don't bother with an IPI, just see if we
>> +	 * have more to push.
>> +	 */
>> +	if (unlikely(cpu == rq->cpu))
>> +		goto again;
>> +
>> +	/* Try the next RT overloaded CPU */
>> +	irq_work_queue_on(&dl_rq->push_work, cpu);
>> +}
>> +
>> +static void push_irq_work_func(struct irq_work *work)
>> +{
>> +	struct dl_rq *dl_rq = container_of(work, struct dl_rq, push_work);
>> +
>> +	try_to_push_tasks(dl_rq);
>> +}
>> +#endif /* HAVE_RT_PUSH_IPI */
>> +
>>  static int pull_dl_task(struct rq *this_rq)
>>  {
>>  	int this_cpu = this_rq->cpu, ret = 0, cpu;
>> @@ -1432,6 +1602,13 @@ static int pull_dl_task(struct rq *this_rq)
>>  	 */
>>  	smp_rmb();
>>  
>> +#ifdef HAVE_RT_PUSH_IPI
>> +	if (sched_feat(RT_PUSH_IPI)) {
>> +		tell_cpu_to_push(this_rq);
>> +		return 0;
>> +	}
>> +#endif
>> +
>>  	for_each_cpu(cpu, this_rq->rd->dlo_mask) {
>>  		if (this_cpu == cpu)
>>  			continue;
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index dd532c5..87a937c 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -500,6 +500,12 @@ struct dl_rq {
>>  	 */
>>  	struct rb_root pushable_dl_tasks_root;
>>  	struct rb_node *pushable_dl_tasks_leftmost;
>> +#ifdef HAVE_RT_PUSH_IPI
>> +	int push_flags;
>> +	int push_cpu;
>> +	struct irq_work push_work;
>> +	raw_spinlock_t push_lock;
>> +#endif
>>  #else
>>  	struct dl_bw dl_bw;
>>  #endif