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Subject[RFC][PATCH 04/22] sched: SCHED_DEADLINE SMP-related data structures
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Introduce data structures relevant for implementing dynamic
migration of -deadline tasks.

Mainly, this is the logic for checking if runqueues are
overloaded with -deadline tasks and for choosing where
a task should migrate, when it is the case.

Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Dario Faggioli <raistlin@linux.it>
---
include/linux/sched.h | 1 +
kernel/sched.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 58 insertions(+), 1 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c72a132..f94da51 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1336,6 +1336,7 @@ struct task_struct {

struct list_head tasks;
struct plist_node pushable_tasks;
+ struct rb_node pushable_dl_tasks;

struct mm_struct *mm, *active_mm;
#if defined(SPLIT_RSS_COUNTING)
diff --git a/kernel/sched.c b/kernel/sched.c
index d157358..b11e888 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -424,6 +424,35 @@ struct dl_rq {
struct rb_node *rb_leftmost;

unsigned long dl_nr_running;
+
+#ifdef CONFIG_SMP
+ /*
+ * Deadline values of the currently executing and the
+ * earliest ready task on this rq. Caching these facilitates
+ * the decision wether or not a ready but not running task
+ * should migrate somewhere else.
+ */
+ struct {
+ u64 curr;
+ u64 next;
+ } earliest_dl;
+
+ unsigned long dl_nr_migratory;
+ unsigned long dl_nr_total;
+ int overloaded;
+
+ /*
+ * Tasks on this rq that can be pushed away. They are kept in
+ * an rb-tree, ordered by tasks' deadlines, with caching
+ * of the leftmost (earliest deadline) element.
+ */
+ struct rb_root pushable_dl_tasks_root;
+ struct rb_node *pushable_dl_tasks_leftmost;
+#endif
+
+#ifdef CONFIG_DEADLINE_GROUP_SCHED
+ struct rq *rq;
+#endif
};

#ifdef CONFIG_SMP
@@ -442,6 +471,13 @@ struct root_domain {
cpumask_var_t online;

/*
+ * The bit corresponding to a CPU gets set here if such CPU has more
+ * than one runnable -deadline task (as it is below for RT tasks).
+ */
+ cpumask_var_t dlo_mask;
+ atomic_t dlo_count;
+
+ /*
* The "RT overload" flag: it gets set if a CPU has more than
* one runnable RT task.
*/
@@ -2742,6 +2778,7 @@ void sched_fork(struct task_struct *p, int clone_flags)
/* Want to start with kernel preemption disabled. */
task_thread_info(p)->preempt_count = 1;
#endif
+ RB_CLEAR_NODE(&p->pushable_dl_tasks);
plist_node_init(&p->pushable_tasks, MAX_PRIO);

put_cpu();
@@ -5804,6 +5841,7 @@ again:
p->sched_class->set_cpus_allowed(p, new_mask);
else {
cpumask_copy(&p->cpus_allowed, new_mask);
+ p->dl.nr_cpus_allowed = cpumask_weight(new_mask);
p->rt.nr_cpus_allowed = cpumask_weight(new_mask);
}

@@ -6551,6 +6589,7 @@ static void free_rootdomain(struct root_domain *rd)

cpupri_cleanup(&rd->cpupri);

+ free_cpumask_var(rd->dlo_mask);
free_cpumask_var(rd->rto_mask);
free_cpumask_var(rd->online);
free_cpumask_var(rd->span);
@@ -6602,8 +6641,10 @@ static int init_rootdomain(struct root_domain *rd)
goto out;
if (!alloc_cpumask_var(&rd->online, GFP_KERNEL))
goto free_span;
- if (!alloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
+ if (!alloc_cpumask_var(&rd->dlo_mask, GFP_KERNEL))
goto free_online;
+ if (!alloc_cpumask_var(&rd->rto_mask, GFP_KERNEL))
+ goto free_dlo_mask;

if (cpupri_init(&rd->cpupri) != 0)
goto free_rto_mask;
@@ -6611,6 +6652,8 @@ static int init_rootdomain(struct root_domain *rd)

free_rto_mask:
free_cpumask_var(rd->rto_mask);
+free_dlo_mask:
+ free_cpumask_var(rd->dlo_mask);
free_online:
free_cpumask_var(rd->online);
free_span:
@@ -8033,6 +8076,19 @@ static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
static void init_dl_rq(struct dl_rq *dl_rq, struct rq *rq)
{
dl_rq->rb_root = RB_ROOT;
+
+#ifdef CONFIG_SMP
+ /* zero means no -deadline tasks */
+ dl_rq->earliest_dl.curr = dl_rq->earliest_dl.next = 0;
+
+ dl_rq->dl_nr_migratory = 0;
+ dl_rq->overloaded = 0;
+ dl_rq->pushable_dl_tasks_root = RB_ROOT;
+#endif
+
+#ifdef CONFIG_DEADLINE_GROUP_SCHED
+ dl_rq->rq = rq;
+#endif
}

#ifdef CONFIG_FAIR_GROUP_SCHED
--
1.7.2.3

--
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy)
http://blog.linux.it/raistlin / raistlin@ekiga.net /
dario.faggioli@jabber.org
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