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Date: Wed, 5 Nov 2014 23:48:23 +0800
From: "pang.xunlei" <pang.xunlei@...aro.org>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Juri Lelli <juri.lelli@...il.com>,
"pang.xunlei" <pang.xunlei@...aro.org>
Subject: [PATCH v3 4/7] sched/deadline: Fix several problems with cpudl_find()
cpudl_find() has some problems:
1)in check_preempt_equal_dl(), called with NULL later_mask, thus
cpudl_find() doesn't check cpudl.free_cpus at all.
2)Also, the whole system isn't always overloaded with many DL tasks
in which cases all the cpu may have a DL task running, so it may
return the best cpu, because we only return the first maximum deadline
cpu(is there a need to iterate the same deadline value to find more
different cpus if possible?).
So it may be reasonable to change the return value of cpudl_find()
to a bool type, because it isn't always the best cpu actually which
can be better determined in find_later_rq() via sched_domain topology.
3)in the "else if" branch, uses cpus_allowed to test again.
This patch syncs the logic in a former patch by "Juri Lelli", then
problem 1) will be solved naturally, and modifies cpudl_find() and
all its call sites to address these problems.
The former patch by "Juri Lelli" is:
"sched/deadline: Fix inter- exclusive cpusets migrations"
Signed-off-by: pang.xunlei <pang.xunlei@...aro.org>
---
kernel/sched/cpudeadline.c | 29 ++++++++++++++---------------
kernel/sched/cpudeadline.h | 2 +-
kernel/sched/deadline.c | 45 ++++++++++++++++++++++++++-------------------
3 files changed, 41 insertions(+), 35 deletions(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 539ca3c..72a3da3 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -97,30 +97,29 @@ static inline int cpudl_maximum(struct cpudl *cp)
* 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)
+ * @later_mask: a mask used to filter cpus, also used to fill
+ * in with the selected CPUs if set_flag is set. Not NULL.
+ * @set_flag: a flag to determine if should set the later_mask.
*
- * Returns: int - best CPU (heap maximum if suitable)
+ * Returns: (int)bool - CPUs were found
*/
int cpudl_find(struct cpudl *cp, struct task_struct *p,
- struct cpumask *later_mask)
+ struct cpumask *later_mask, int set_flag)
{
- int best_cpu = -1;
+ struct cpumask tmp_mask;
const struct sched_dl_entity *dl_se = &p->dl;
- if (later_mask && cpumask_and(later_mask, later_mask, cp->free_cpus)) {
- best_cpu = cpumask_any(later_mask);
- goto out;
- } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) &&
+
+ if (cpumask_and(&tmp_mask, later_mask, cp->free_cpus)) {
+ if (set_flag)
+ cpumask_copy(later_mask, &tmp_mask);
+ return 1;
+ } else if (cpumask_and(later_mask, later_mask, cpumask_of(cpudl_maximum(cp))) &&
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);
+ return 1;
}
-out:
- WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
-
- return best_cpu;
+ return 0;
}
/*
diff --git a/kernel/sched/cpudeadline.h b/kernel/sched/cpudeadline.h
index 538c979..0c9636e 100644
--- a/kernel/sched/cpudeadline.h
+++ b/kernel/sched/cpudeadline.h
@@ -21,7 +21,7 @@ struct cpudl {
#ifdef CONFIG_SMP
int cpudl_find(struct cpudl *cp, struct task_struct *p,
- struct cpumask *later_mask);
+ struct cpumask *later_mask, int set_flag);
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);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 256e577..42edfcd 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -946,23 +946,34 @@ out:
return cpu;
}
+static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
+
static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
{
+ struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
+
/*
* Current can't be migrated, useless to reschedule,
* let's hope p can move out.
*/
- if (rq->curr->nr_cpus_allowed == 1 ||
- cpudl_find(&rq->rd->cpudl, rq->curr, NULL) == -1)
+ if (rq->curr->nr_cpus_allowed == 1)
+ return;
+
+ cpumask_and(later_mask, rq->rd->span, cpu_active_mask);
+ cpumask_and(later_mask, later_mask, &rq->curr->cpus_allowed);
+ if (!cpudl_find(&rq->rd->cpudl, rq->curr, later_mask, 0))
return;
/*
* p is migratable, so let's not schedule it and
* see if it is pushed or pulled somewhere else.
*/
- if (p->nr_cpus_allowed != 1 &&
- cpudl_find(&rq->rd->cpudl, p, NULL) != -1)
- return;
+ if (p->nr_cpus_allowed != 1) {
+ cpumask_and(later_mask, rq->rd->span, cpu_active_mask);
+ cpumask_and(later_mask, later_mask, &p->cpus_allowed);
+ if (cpudl_find(&rq->rd->cpudl, p, later_mask, 0))
+ return;
+ }
resched_curr(rq);
}
@@ -1148,14 +1159,12 @@ next_node:
return NULL;
}
-static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
-
static int find_later_rq(struct task_struct *task)
{
struct sched_domain *sd;
struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
int this_cpu = smp_processor_id();
- int best_cpu, cpu = task_cpu(task);
+ int cpu = task_cpu(task);
/* Make sure the mask is initialized first */
if (unlikely(!later_mask))
@@ -1168,14 +1177,14 @@ static int find_later_rq(struct task_struct *task)
* We have to consider system topology and task affinity
* first, then we can look for a suitable cpu.
*/
- cpumask_copy(later_mask, task_rq(task)->rd->span);
- cpumask_and(later_mask, later_mask, cpu_active_mask);
+ cpumask_and(later_mask, task_rq(task)->rd->span, cpu_active_mask);
cpumask_and(later_mask, later_mask, &task->cpus_allowed);
- best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
- task, later_mask);
- if (best_cpu == -1)
+ if (!cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask, 1))
return -1;
+ if (cpumask_weight(later_mask) == 1)
+ return cpumask_any(later_mask);
+
/*
* If we are here, some target has been found,
* the most suitable of which is cached in best_cpu.
@@ -1200,6 +1209,7 @@ static int find_later_rq(struct task_struct *task)
rcu_read_lock();
for_each_domain(cpu, sd) {
+ int best_cpu;
if (sd->flags & SD_WAKE_AFFINE) {
/*
@@ -1212,12 +1222,9 @@ static int find_later_rq(struct task_struct *task)
return this_cpu;
}
- /*
- * Last chance: if best_cpu is valid and is
- * in the mask, that becomes our choice.
- */
- if (best_cpu < nr_cpu_ids &&
- cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
+ best_cpu = cpumask_first_and(later_mask,
+ sched_domain_span(sd));
+ if (best_cpu < nr_cpu_ids) {
rcu_read_unlock();
return best_cpu;
}
--
2.1.0
--
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