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Commit 6bfd6d72 authored by Juri Lelli's avatar Juri Lelli Committed by Ingo Molnar
Browse files

sched/deadline: speed up SCHED_DEADLINE pushes with a push-heap 

Data from tests confirmed that the original active load balancing
logic didn't scale neither in the number of CPU nor in the number of
tasks (as sched_rt does).

Here we provide a global data structure to keep track of deadlines
of the running tasks in the system. The structure is composed by
a bitmask showing the free CPUs and a max-heap, needed when the system
is heavily loaded.

The implementation and concurrent access scheme are kept simple by
design. However, our measurements show that we can compete with sched_rt
on large multi-CPUs machines [1].

Only the push path is addressed, the extension to use this structure
also for pull decisions is straightforward. However, we are currently
evaluating different (in order to decrease/avoid contention) data
structures to solve possibly both problems. We are also going to re-run
tests considering recent changes inside cpupri [2].

 [1] http://retis.sssup.it/~jlelli/papers/Ospert11Lelli.pdf
 [2] http://www.spinics.net/lists/linux-rt-users/msg06778.html



Signed-off-by: default avatarJuri Lelli <juri.lelli@gmail.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-14-git-send-email-juri.lelli@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 332ac17e

kernel/sched/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -14,7 +14,7 @@ endif 
obj-y += core.o proc.o clock.o cputime.o

obj-y += idle_task.o fair.o rt.o deadline.o stop_task.o

obj-y += wait.o completion.o

obj-$(CONFIG_SMP) += cpupri.o

obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o

obj-$(CONFIG_SCHED_AUTOGROUP) += auto_group.o

obj-$(CONFIG_SCHEDSTATS) += stats.o

obj-$(CONFIG_SCHED_DEBUG) += debug.o

kernel/sched/core.c

+3 −0
Original line number Diff line number Diff line
@@ -5287,6 +5287,7 @@ static void free_rootdomain(struct rcu_head *rcu) 
	struct root_domain *rd = container_of(rcu, struct root_domain, rcu);



	cpupri_cleanup(&rd->cpupri);

	cpudl_cleanup(&rd->cpudl);

	free_cpumask_var(rd->dlo_mask);

	free_cpumask_var(rd->rto_mask);

	free_cpumask_var(rd->online);
@@ -5345,6 +5346,8 @@ static int init_rootdomain(struct root_domain *rd) 
		goto free_dlo_mask;



	init_dl_bw(&rd->dl_bw);

	if (cpudl_init(&rd->cpudl) != 0)

		goto free_dlo_mask;



	if (cpupri_init(&rd->cpupri) != 0)

		goto free_rto_mask;

kernel/sched/cpudeadline.c

0 → 100644
+216 −0
Original line number Diff line number Diff line 
/*

 *  kernel/sched/cpudl.c

 *

 *  Global CPU deadline management

 *

 *  Author: Juri Lelli <j.lelli@sssup.it>

 *

 *  This program is free software; you can redistribute it and/or

 *  modify it under the terms of the GNU General Public License

 *  as published by the Free Software Foundation; version 2

 *  of the License.

 */



#include <linux/gfp.h>

#include <linux/kernel.h>

#include "cpudeadline.h"



static inline int parent(int i)

{

	return (i - 1) >> 1;

}



static inline int left_child(int i)

{

	return (i << 1) + 1;

}



static inline int right_child(int i)

{

	return (i << 1) + 2;

}



static inline int dl_time_before(u64 a, u64 b)

{

	return (s64)(a - b) < 0;

}



void cpudl_exchange(struct cpudl *cp, int a, int b)

{

	int cpu_a = cp->elements[a].cpu, cpu_b = cp->elements[b].cpu;



	swap(cp->elements[a], cp->elements[b]);

	swap(cp->cpu_to_idx[cpu_a], cp->cpu_to_idx[cpu_b]);

}



void cpudl_heapify(struct cpudl *cp, int idx)

{

	int l, r, largest;



	/* adapted from lib/prio_heap.c */

	while(1) {

		l = left_child(idx);

		r = right_child(idx);

		largest = idx;



		if ((l < cp->size) && dl_time_before(cp->elements[idx].dl,

							cp->elements[l].dl))

			largest = l;

		if ((r < cp->size) && dl_time_before(cp->elements[largest].dl,

							cp->elements[r].dl))

			largest = r;

		if (largest == idx)

			break;



		/* Push idx down the heap one level and bump one up */

		cpudl_exchange(cp, largest, idx);

		idx = largest;

	}

}



void cpudl_change_key(struct cpudl *cp, int idx, u64 new_dl)

{

	WARN_ON(idx > num_present_cpus() || idx == IDX_INVALID);



	if (dl_time_before(new_dl, cp->elements[idx].dl)) {

		cp->elements[idx].dl = new_dl;

		cpudl_heapify(cp, idx);

	} else {

		cp->elements[idx].dl = new_dl;

		while (idx > 0 && dl_time_before(cp->elements[parent(idx)].dl,

					cp->elements[idx].dl)) {

			cpudl_exchange(cp, idx, parent(idx));

			idx = parent(idx);

		}

	}

}



static inline int cpudl_maximum(struct cpudl *cp)

{

	return cp->elements[0].cpu;

}



/*

 * cpudl_find - find the best (later-dl) CPU in the system

 * @cp: the cpudl max-heap context

 * @p: the task

 * @later_mask: a mask to fill in with the selected CPUs (or NULL)

 *

 * Returns: int - best CPU (heap maximum if suitable)

 */

int cpudl_find(struct cpudl *cp, struct task_struct *p,

	       struct cpumask *later_mask)

{

	int best_cpu = -1;

	const struct sched_dl_entity *dl_se = &p->dl;



	if (later_mask && cpumask_and(later_mask, cp->free_cpus,

			&p->cpus_allowed) && cpumask_and(later_mask,

			later_mask, cpu_active_mask)) {

		best_cpu = cpumask_any(later_mask);

		goto out;

	} else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&

			dl_time_before(dl_se->deadline, cp->elements[0].dl)) {

		best_cpu = cpudl_maximum(cp);

		if (later_mask)

			cpumask_set_cpu(best_cpu, later_mask);

	}



out:

	WARN_ON(best_cpu > num_present_cpus() && best_cpu != -1);



	return best_cpu;

}



/*

 * cpudl_set - update the cpudl max-heap

 * @cp: the cpudl max-heap context

 * @cpu: the target cpu

 * @dl: the new earliest deadline for this cpu

 *

 * Notes: assumes cpu_rq(cpu)->lock is locked

 *

 * Returns: (void)

 */

void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid)

{

	int old_idx, new_cpu;

	unsigned long flags;



	WARN_ON(cpu > num_present_cpus());



	raw_spin_lock_irqsave(&cp->lock, flags);

	old_idx = cp->cpu_to_idx[cpu];

	if (!is_valid) {

		/* remove item */

		if (old_idx == IDX_INVALID) {

			/*

			 * Nothing to remove if old_idx was invalid.

			 * This could happen if a rq_offline_dl is

			 * called for a CPU without -dl tasks running.

			 */

			goto out;

		}

		new_cpu = cp->elements[cp->size - 1].cpu;

		cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;

		cp->elements[old_idx].cpu = new_cpu;

		cp->size--;

		cp->cpu_to_idx[new_cpu] = old_idx;

		cp->cpu_to_idx[cpu] = IDX_INVALID;

		while (old_idx > 0 && dl_time_before(

				cp->elements[parent(old_idx)].dl,

				cp->elements[old_idx].dl)) {

			cpudl_exchange(cp, old_idx, parent(old_idx));

			old_idx = parent(old_idx);

		}

		cpumask_set_cpu(cpu, cp->free_cpus);

                cpudl_heapify(cp, old_idx);



		goto out;

	}



	if (old_idx == IDX_INVALID) {

		cp->size++;

		cp->elements[cp->size - 1].dl = 0;

		cp->elements[cp->size - 1].cpu = cpu;

		cp->cpu_to_idx[cpu] = cp->size - 1;

		cpudl_change_key(cp, cp->size - 1, dl);

		cpumask_clear_cpu(cpu, cp->free_cpus);

	} else {

		cpudl_change_key(cp, old_idx, dl);

	}



out:

	raw_spin_unlock_irqrestore(&cp->lock, flags);

}



/*

 * cpudl_init - initialize the cpudl structure

 * @cp: the cpudl max-heap context

 */

int cpudl_init(struct cpudl *cp)

{

	int i;



	memset(cp, 0, sizeof(*cp));

	raw_spin_lock_init(&cp->lock);

	cp->size = 0;

	for (i = 0; i < NR_CPUS; i++)

		cp->cpu_to_idx[i] = IDX_INVALID;

	if (!alloc_cpumask_var(&cp->free_cpus, GFP_KERNEL))

		return -ENOMEM;

	cpumask_setall(cp->free_cpus);



	return 0;

}



/*

 * cpudl_cleanup - clean up the cpudl structure

 * @cp: the cpudl max-heap context

 */

void cpudl_cleanup(struct cpudl *cp)

{

	/*

	 * nothing to do for the moment

	 */

}

kernel/sched/cpudeadline.h

0 → 100644
+33 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_CPUDL_H

#define _LINUX_CPUDL_H



#include <linux/sched.h>



#define IDX_INVALID     -1



struct array_item {

	u64 dl;

	int cpu;

};



struct cpudl {

	raw_spinlock_t lock;

	int size;

	int cpu_to_idx[NR_CPUS];

	struct array_item elements[NR_CPUS];

	cpumask_var_t free_cpus;

};





#ifdef CONFIG_SMP

int cpudl_find(struct cpudl *cp, struct task_struct *p,

	       struct cpumask *later_mask);

void cpudl_set(struct cpudl *cp, int cpu, u64 dl, int is_valid);

int cpudl_init(struct cpudl *cp);

void cpudl_cleanup(struct cpudl *cp);

#else

#define cpudl_set(cp, cpu, dl) do { } while (0)

#define cpudl_init() do { } while (0)

#endif /* CONFIG_SMP */



#endif /* _LINUX_CPUDL_H */

kernel/sched/deadline.c

+14 −39
Original line number Diff line number Diff line
@@ -16,6 +16,8 @@ 
 */

#include "sched.h"



#include <linux/slab.h>



struct dl_bandwidth def_dl_bandwidth;



static inline struct task_struct *dl_task_of(struct sched_dl_entity *dl_se)
@@ -640,6 +642,7 @@ static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) 
		 */

		dl_rq->earliest_dl.next = dl_rq->earliest_dl.curr;

		dl_rq->earliest_dl.curr = deadline;

		cpudl_set(&rq->rd->cpudl, rq->cpu, deadline, 1);

	} else if (dl_rq->earliest_dl.next == 0 ||

		   dl_time_before(deadline, dl_rq->earliest_dl.next)) {

		/*
@@ -663,6 +666,7 @@ static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) 
	if (!dl_rq->dl_nr_running) {

		dl_rq->earliest_dl.curr = 0;

		dl_rq->earliest_dl.next = 0;

		cpudl_set(&rq->rd->cpudl, rq->cpu, 0, 0);

	} else {

		struct rb_node *leftmost = dl_rq->rb_leftmost;

		struct sched_dl_entity *entry;
@@ -670,6 +674,7 @@ static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) 
		entry = rb_entry(leftmost, struct sched_dl_entity, rb_node);

		dl_rq->earliest_dl.curr = entry->deadline;

		dl_rq->earliest_dl.next = next_deadline(rq);

		cpudl_set(&rq->rd->cpudl, rq->cpu, entry->deadline, 1);

	}

}
@@ -855,9 +860,6 @@ static void yield_task_dl(struct rq *rq) 
#ifdef CONFIG_SMP



static int find_later_rq(struct task_struct *task);

static int latest_cpu_find(struct cpumask *span,

			   struct task_struct *task,

			   struct cpumask *later_mask);



static int

select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
@@ -904,7 +906,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p) 
	 * let's hope p can move out.

	 */

	if (rq->curr->nr_cpus_allowed == 1 ||

	    latest_cpu_find(rq->rd->span, rq->curr, NULL) == -1)

	    cpudl_find(&rq->rd->cpudl, rq->curr, NULL) == -1)

		return;



	/*
@@ -912,7 +914,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p) 
	 * see if it is pushed or pulled somewhere else.

	 */

	if (p->nr_cpus_allowed != 1 &&

	    latest_cpu_find(rq->rd->span, p, NULL) != -1)

	    cpudl_find(&rq->rd->cpudl, p, NULL) != -1)

		return;



	resched_task(rq->curr);
@@ -1085,39 +1087,6 @@ static struct task_struct *pick_next_earliest_dl_task(struct rq *rq, int cpu) 
	return NULL;

}



static int latest_cpu_find(struct cpumask *span,

			   struct task_struct *task,

			   struct cpumask *later_mask)

{

	const struct sched_dl_entity *dl_se = &task->dl;

	int cpu, found = -1, best = 0;

	u64 max_dl = 0;



	for_each_cpu(cpu, span) {

		struct rq *rq = cpu_rq(cpu);

		struct dl_rq *dl_rq = &rq->dl;



		if (cpumask_test_cpu(cpu, &task->cpus_allowed) &&

		    (!dl_rq->dl_nr_running || dl_time_before(dl_se->deadline,

		     dl_rq->earliest_dl.curr))) {

			if (later_mask)

				cpumask_set_cpu(cpu, later_mask);

			if (!best && !dl_rq->dl_nr_running) {

				best = 1;

				found = cpu;

			} else if (!best &&

				   dl_time_before(max_dl,

						  dl_rq->earliest_dl.curr)) {

				max_dl = dl_rq->earliest_dl.curr;

				found = cpu;

			}

		} else if (later_mask)

			cpumask_clear_cpu(cpu, later_mask);

	}



	return found;

}



static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);



static int find_later_rq(struct task_struct *task)
@@ -1134,7 +1103,8 @@ static int find_later_rq(struct task_struct *task) 
	if (task->nr_cpus_allowed == 1)

		return -1;



	best_cpu = latest_cpu_find(task_rq(task)->rd->span, task, later_mask);

	best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,

			task, later_mask);

	if (best_cpu == -1)

		return -1;
@@ -1510,6 +1480,9 @@ static void rq_online_dl(struct rq *rq) 
{

	if (rq->dl.overloaded)

		dl_set_overload(rq);



	if (rq->dl.dl_nr_running > 0)

		cpudl_set(&rq->rd->cpudl, rq->cpu, rq->dl.earliest_dl.curr, 1);

}



/* Assumes rq->lock is held */
@@ -1517,6 +1490,8 @@ static void rq_offline_dl(struct rq *rq) 
{

	if (rq->dl.overloaded)

		dl_clear_overload(rq);



	cpudl_set(&rq->rd->cpudl, rq->cpu, 0, 0);

}



void init_sched_dl_class(void)