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authorDaniel Bristot de Oliveira <bristot@redhat.com>2017-06-26 17:07:15 +0200
committerAlex Shi <alex.shi@linaro.org>2017-12-12 15:26:15 +0800
commitb0220c5dcd59e70e8ef3f78c10d92f06198dd366 (patch)
tree6ba2f4f3af66081d94d17ef2d5165f670770fcd3
parentce1ccaa1e3baf2c8e0f397e98114511f1c11699c (diff)
downloadlinux-linaro-stable-linux-linaro-lsk-v4.14-test.tar.gz
rt: Increase/decrease the nr of migratory tasks when enabling/disabling migrationlinux-linaro-lsk-v4.14-test
There is a problem in the migrate_disable()/enable() implementation regarding the number of migratory tasks in the rt/dl RQs. The problem is the following: When a task is attached to the rt runqueue, it is checked if it either can run in more than one CPU, or if it is with migration disable. If either check is true, the rt_rq->rt_nr_migratory counter is not increased. The counter increases otherwise. When the task is detached, the same check is done. If either check is true, the rt_rq->rt_nr_migratory counter is not decreased. The counter decreases otherwise. The same check is done in the dl scheduler. One important thing is that, migrate disable/enable does not touch this counter for tasks attached to the rt rq. So suppose the following chain of events. Assumptions: Task A is the only runnable task in A Task B runs on the CPU B Task A runs on CFS (non-rt) Task B has RT priority Thus, rt_nr_migratory is 0 B is running Task A can run on all CPUS. Timeline: CPU A/TASK A CPU B/TASK B A takes the rt mutex X . A disables migration . . B tries to take the rt mutex X . As it is held by A { . A inherits the rt priority of B . A is dequeued from CFS RQ of CPU A . A is enqueued in the RT RQ of CPU A . As migration is disabled . rt_nr_migratory in A is not increased . A enables migration A releases the rt mutex X { A returns to its original priority A ask to be dequeued from RT RQ { As migration is now enabled and it can run on all CPUS { rt_nr_migratory should be decreased As rt_nr_migratory is 0, rt_nr_migratory under flows } } This variable is important because it notifies if there are more than one runnable & migratory task in the runqueue. If there are more than one tasks, the rt_rq is set as overloaded, and then tries to migrate some tasks. This rule is important to keep the scheduler working conserving, that is, in a system with M CPUs, the M highest priority tasks should be running. As rt_nr_migratory is unsigned, it will become > 0, notifying that the RQ is overloaded, activating pushing mechanism without need. This patch fixes this problem by decreasing/increasing the rt/dl_nr_migratory in the migrate disable/enable operations. Reported-by: Pei Zhang <pezhang@redhat.com> Reported-by: Luiz Capitulino <lcapitulino@redhat.com> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Luis Claudio R. Goncalves <lgoncalv@redhat.com> Cc: Clark Williams <williams@redhat.com> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: LKML <linux-kernel@vger.kernel.org> Cc: linux-rt-users <linux-rt-users@vger.kernel.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> (cherry picked from commit 1e2a758a08a3326c8309c5e2e98c1943935e797d) Signed-off-by: Alex Shi <alex.shi@linaro.org>
-rw-r--r--kernel/sched/core.c49
1 files changed, 44 insertions, 5 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 00da096..415db11 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6837,6 +6837,47 @@ const u32 sched_prio_to_wmult[40] = {
#if defined(CONFIG_PREEMPT_COUNT) && defined(CONFIG_SMP)
+static inline void
+update_nr_migratory(struct task_struct *p, long delta)
+{
+ if (unlikely((p->sched_class == &rt_sched_class ||
+ p->sched_class == &dl_sched_class) &&
+ p->nr_cpus_allowed > 1)) {
+ if (p->sched_class == &rt_sched_class)
+ task_rq(p)->rt.rt_nr_migratory += delta;
+ else
+ task_rq(p)->dl.dl_nr_migratory += delta;
+ }
+}
+
+static inline void
+migrate_disable_update_cpus_allowed(struct task_struct *p)
+{
+ struct rq *rq;
+ struct rq_flags rf;
+
+ p->cpus_ptr = cpumask_of(smp_processor_id());
+
+ rq = task_rq_lock(p, &rf);
+ update_nr_migratory(p, -1);
+ p->nr_cpus_allowed = 1;
+ task_rq_unlock(rq, p, &rf);
+}
+
+static inline void
+migrate_enable_update_cpus_allowed(struct task_struct *p)
+{
+ struct rq *rq;
+ struct rq_flags rf;
+
+ p->cpus_ptr = &p->cpus_mask;
+
+ rq = task_rq_lock(p, &rf);
+ p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);
+ update_nr_migratory(p, 1);
+ task_rq_unlock(rq, p, &rf);
+}
+
void migrate_disable(void)
{
struct task_struct *p = current;
@@ -6857,10 +6898,9 @@ void migrate_disable(void)
}
preempt_disable();
- p->migrate_disable = 1;
- p->cpus_ptr = cpumask_of(smp_processor_id());
- p->nr_cpus_allowed = 1;
+ migrate_disable_update_cpus_allowed(p);
+ p->migrate_disable = 1;
preempt_enable();
}
@@ -6889,9 +6929,8 @@ void migrate_enable(void)
preempt_disable();
- p->cpus_ptr = &p->cpus_mask;
- p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);
p->migrate_disable = 0;
+ migrate_enable_update_cpus_allowed(p);
if (p->migrate_disable_update) {
struct rq *rq;