Re: [RFC][PATCH] fix SCHED_FIFO spec violation (backport)

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Thu, 2008-07-03 at 15:41 -0700, Darren Hart wrote:
> Enqueue deprioritized RT tasks to head of prio array
> 
> This patch backports Peter Z's enqueue to head of prio array on 
> de-prioritization to 2.6.24.7-rt14 which doesn't have the 
> enqueue_rt_entity and associated changes.
> 
> I've run several long running real-time java benchmarks and it's
> holding so far.  Steven, please consider this patch for inclusion
> in the next 2.6.24.7-rtX release.
> 
> Peter, I didn't include your Signed-off-by as only about half your
> original patch applied to 2.6.24.7-r14.  If you're happy with this
> version, would you also sign off?

Sure thing,

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

(Thanks for pointing me at this John, I completely missed it)..

> Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
> 
> 
> ---
> Index: linux-2.6.24.7-ibmrt2.6-view/include/linux/sched.h
> ===================================================================
> --- linux-2.6.24.7-ibmrt2.6-view.orig/include/linux/sched.h
> +++ linux-2.6.24.7-ibmrt2.6-view/include/linux/sched.h
> @@ -897,11 +897,16 @@ struct uts_namespace;
>  struct rq;
>  struct sched_domain;
>  
> +#define ENQUEUE_WAKEUP	0x01
> +#define ENQUEUE_HEAD	0x02
> +
> +#define DEQUEUE_SLEEP	0x01
> +
>  struct sched_class {
>  	const struct sched_class *next;
>  
> -	void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup);
> -	void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep);
> +	void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags);
> +	void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);
>  	void (*yield_task) (struct rq *rq);
>  	int  (*select_task_rq)(struct task_struct *p, int sync);
>  
> Index: linux-2.6.24.7-ibmrt2.6-view/kernel/sched.c
> ===================================================================
> --- linux-2.6.24.7-ibmrt2.6-view.orig/kernel/sched.c
> +++ linux-2.6.24.7-ibmrt2.6-view/kernel/sched.c
> @@ -1046,7 +1046,7 @@ static const u32 prio_to_wmult[40] = {
>   /*  15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
>  };
>  
> -static void activate_task(struct rq *rq, struct task_struct *p, int wakeup);
> +static void activate_task(struct rq *rq, struct task_struct *p, int flags);
>  
>  /*
>   * runqueue iterator, to support SMP load-balancing between different
> @@ -1155,16 +1155,16 @@ static void set_load_weight(struct task_
>  	p->se.load.inv_weight = prio_to_wmult[p->static_prio - MAX_RT_PRIO];
>  }
>  
> -static void enqueue_task(struct rq *rq, struct task_struct *p, int wakeup)
> +static void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	sched_info_queued(p);
> -	p->sched_class->enqueue_task(rq, p, wakeup);
> +	p->sched_class->enqueue_task(rq, p, flags);
>  	p->se.on_rq = 1;
>  }
>  
> -static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
> +static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
>  {
> -	p->sched_class->dequeue_task(rq, p, sleep);
> +	p->sched_class->dequeue_task(rq, p, flags);
>  	p->se.on_rq = 0;
>  }
>  
> @@ -1219,26 +1219,26 @@ static int effective_prio(struct task_st
>  /*
>   * activate_task - move a task to the runqueue.
>   */
> -static void activate_task(struct rq *rq, struct task_struct *p, int wakeup)
> +static void activate_task(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	if (p->state == TASK_UNINTERRUPTIBLE)
>  		rq->nr_uninterruptible--;
>  
>  	ftrace_event_task_activate(p, cpu_of(rq));
> -	enqueue_task(rq, p, wakeup);
> +	enqueue_task(rq, p, flags);
>  	inc_nr_running(p, rq);
>  }
>  
>  /*
>   * deactivate_task - remove a task from the runqueue.
>   */
> -static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
> +static void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	if (p->state == TASK_UNINTERRUPTIBLE)
>  		rq->nr_uninterruptible++;
>  
>  	ftrace_event_task_deactivate(p, cpu_of(rq));
> -	dequeue_task(rq, p, sleep);
> +	dequeue_task(rq, p, flags);
>  	dec_nr_running(p, rq);
>  }
>  
> @@ -1759,7 +1759,7 @@ out_activate:
>  	else
>  		schedstat_inc(p, se.nr_wakeups_remote);
>  	update_rq_clock(rq);
> -	activate_task(rq, p, 1);
> +	activate_task(rq, p, ENQUEUE_WAKEUP);
>  	check_preempt_curr(rq, p);
>  	success = 1;
>  
> @@ -3968,7 +3968,7 @@ asmlinkage void __sched __schedule(void)
>  			prev->state = TASK_RUNNING;
>  		} else {
>  			touch_softlockup_watchdog();
> -			deactivate_task(rq, prev, 1);
> +			deactivate_task(rq, prev, DEQUEUE_SLEEP);
>  		}
>  		switch_count = &prev->nvcsw;
>  	}
> @@ -4431,7 +4431,7 @@ EXPORT_SYMBOL(sleep_on_timeout);
>  void task_setprio(struct task_struct *p, int prio)
>  {
>  	unsigned long flags;
> -	int oldprio, prev_resched, on_rq, running;
> +	int oldprio, prev_resched, on_rq, running, down;
>  	struct rq *rq;
>  	const struct sched_class *prev_class = p->sched_class;
>  
> @@ -4472,6 +4472,7 @@ void task_setprio(struct task_struct *p,
>  	else
>  		p->sched_class = &fair_sched_class;
>  
> + 	down = (prio > p->prio) ? ENQUEUE_HEAD : 0;
>  	p->prio = prio;
>  
>  //	trace_special_pid(p->pid, __PRIO(oldprio), PRIO(p));
> @@ -4480,7 +4481,7 @@ void task_setprio(struct task_struct *p,
>  	if (running)
>  		p->sched_class->set_curr_task(rq);
>  	if (on_rq) {
> -		enqueue_task(rq, p, 0);
> + 		enqueue_task(rq, p, down);
>  		check_class_changed(rq, p, prev_class, oldprio, running);
>  	}
>  //	trace_special(prev_resched, _need_resched(), 0);
> Index: linux-2.6.24.7-ibmrt2.6-view/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.24.7-ibmrt2.6-view.orig/kernel/sched_fair.c
> +++ linux-2.6.24.7-ibmrt2.6-view/kernel/sched_fair.c
> @@ -756,10 +756,11 @@ static inline struct sched_entity *paren
>   * increased. Here we update the fair scheduling stats and
>   * then put the task into the rbtree:
>   */
> -static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
> +static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	struct cfs_rq *cfs_rq;
>  	struct sched_entity *se = &p->se;
> +	int wakeup = flags & ENQUEUE_WAKEUP;
>  
>  	for_each_sched_entity(se) {
>  		if (se->on_rq)
> @@ -775,10 +776,11 @@ static void enqueue_task_fair(struct rq 
>   * decreased. We remove the task from the rbtree and
>   * update the fair scheduling stats:
>   */
> -static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int sleep)
> +static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	struct cfs_rq *cfs_rq;
>  	struct sched_entity *se = &p->se;
> +	int sleep = flags & DEQUEUE_SLEEP;
>  
>  	for_each_sched_entity(se) {
>  		cfs_rq = cfs_rq_of(se);
> Index: linux-2.6.24.7-ibmrt2.6-view/kernel/sched_idletask.c
> ===================================================================
> --- linux-2.6.24.7-ibmrt2.6-view.orig/kernel/sched_idletask.c
> +++ linux-2.6.24.7-ibmrt2.6-view/kernel/sched_idletask.c
> @@ -31,7 +31,7 @@ static struct task_struct *pick_next_tas
>   * message if some code attempts to do it:
>   */
>  static void
> -dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
> +dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	spin_unlock_irq(&rq->lock);
>  	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
> Index: linux-2.6.24.7-ibmrt2.6-view/kernel/sched_rt.c
> ===================================================================
> --- linux-2.6.24.7-ibmrt2.6-view.orig/kernel/sched_rt.c
> +++ linux-2.6.24.7-ibmrt2.6-view/kernel/sched_rt.c
> @@ -181,11 +181,16 @@ unsigned long rt_nr_uninterruptible_cpu(
>  	return cpu_rq(cpu)->rt.rt_nr_uninterruptible;
>  }
>  
> -static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int wakeup)
> +static void enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	struct rt_prio_array *array = &rq->rt.active;
>  
> -	list_add_tail(&p->run_list, array->queue + p->prio);
> +
> + 	if (unlikely(flags & ENQUEUE_HEAD))
> +		list_add(&p->run_list, array->queue + p->prio);
> + 	else
> +		list_add_tail(&p->run_list, array->queue + p->prio);
> +
>  	__set_bit(p->prio, array->bitmap);
>  	inc_rt_tasks(p, rq);
>  
> @@ -196,7 +201,7 @@ static void enqueue_task_rt(struct rq *r
>  /*
>   * Adding/removing a task to/from a priority array:
>   */
> -static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int sleep)
> +static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	struct rt_prio_array *array = &rq->rt.active;
>  
> @@ -306,7 +311,7 @@ static void put_prev_task_rt(struct rq *
>  #define RT_MAX_TRIES 3
>  
>  static int double_lock_balance(struct rq *this_rq, struct rq *busiest);
> -static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep);
> +static void deactivate_task(struct rq *rq, struct task_struct *p, int flags);
>  
>  static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
>  {
> 
>