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: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1383831828-15501-14-git-send-email-juri.lelli@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Juri Lelli 2013-11-07 14:43:47 +01:00 committed by Ingo Molnar
parent 332ac17ef5
commit 6bfd6d72f5
6 changed files with 269 additions and 40 deletions

View file

@ -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

View file

@ -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;

216
kernel/sched/cpudeadline.c Normal file
View file

@ -0,0 +1,216 @@
/*
* 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
*/
}

View file

@ -0,0 +1,33 @@
#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 */

View file

@ -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 @@ next_node:
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)

View file

@ -10,6 +10,7 @@
#include <linux/slab.h>
#include "cpupri.h"
#include "cpudeadline.h"
#include "cpuacct.h"
struct rq;
@ -503,6 +504,7 @@ struct root_domain {
cpumask_var_t dlo_mask;
atomic_t dlo_count;
struct dl_bw dl_bw;
struct cpudl cpudl;
/*
* The "RT overload" flag: it gets set if a CPU has more than