linux-kernel - [patch 06/10] sched: Add task components for migration control

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Date:   Thu, 17 Sep 2020 11:42:08 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        Qais Yousef <qais.yousef@....com>,
        Scott Wood <swood@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Vincent Donnefort <vincent.donnefort@....com>
Subject: [patch 06/10] sched: Add task components for migration control

The upcoming RT migrate_enable/disable() support will track migrate
disabled state in task_struct.

Add a new migration_ctrl struct to hold all necessary information and add
the required initializers.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/sched.h |   30 +++++++++++++++++++++++++++---
 init/init_task.c      |    3 +++
 kernel/fork.c         |    1 +
 kernel/sched/debug.c  |    4 ++++
 4 files changed, 35 insertions(+), 3 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -628,6 +628,20 @@ struct wake_q_node {
 	struct wake_q_node *next;
 };
 
+#if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
+struct task_migration_ctrl {
+	struct mutex			mutex;
+	int				disable_cnt;
+};
+
+#define INIT_TASK_MIGRATION_CTRL_INITIALIZER				\
+{									\
+	.mutex = __MUTEX_INITIALIZER(init_task.migration_ctrl.mutex),	\
+}
+#else /* CONFIG_PREEMPT_RT && CONFIG_SMP */
+struct task_migration_ctrl { };
+#endif /* !(CONFIG_PREEMPT_RT && CONFIG_SMP) */
+
 struct task_struct {
 #ifdef CONFIG_THREAD_INFO_IN_TASK
 	/*
@@ -713,6 +727,7 @@ struct task_struct {
 	int				nr_cpus_allowed;
 	const cpumask_t			*cpus_ptr;
 	cpumask_t			cpus_mask;
+	struct task_migration_ctrl	migration_ctrl;
 
 #ifdef CONFIG_PREEMPT_RCU
 	int				rcu_read_lock_nesting;
@@ -1865,7 +1880,7 @@ static __always_inline bool need_resched
 }
 
 /*
- * Wrappers for p->thread_info->cpu access. No-op on UP.
+ * Various SMP helper functions. No-ops on UP.
  */
 #ifdef CONFIG_SMP
 
@@ -1880,7 +1895,14 @@ static inline unsigned int task_cpu(cons
 
 extern void set_task_cpu(struct task_struct *p, unsigned int cpu);
 
-#else
+static inline void task_migration_ctrl_init(struct task_struct *p)
+{
+#ifdef CONFIG_PREEMPT_RT
+	mutex_init(&p->migration_ctrl.mutex);
+#endif
+}
+
+#else /* CONFIG_SMP */
 
 static inline unsigned int task_cpu(const struct task_struct *p)
 {
@@ -1891,7 +1913,9 @@ static inline void set_task_cpu(struct t
 {
 }
 
-#endif /* CONFIG_SMP */
+static inline void task_migration_ctrl_init(struct task_struct *p) { }
+
+#endif /* !CONFIG_SMP */
 
 /*
  * In order to reduce various lock holder preemption latencies provide an
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -209,6 +209,9 @@ struct task_struct init_task
 #ifdef CONFIG_SECCOMP
 	.seccomp	= { .filter_count = ATOMIC_INIT(0) },
 #endif
+#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT)
+	.migration_ctrl = INIT_TASK_MIGRATION_CTRL_INITIALIZER,
+#endif
 };
 EXPORT_SYMBOL(init_task);
 
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2119,6 +2119,7 @@ static __latent_entropy struct task_stru
 #ifdef CONFIG_BLOCK
 	p->plug = NULL;
 #endif
+	task_migration_ctrl_init(p);
 	futex_init_task(p);
 
 	/*
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -958,6 +958,10 @@ void proc_sched_show_task(struct task_st
 		P(dl.runtime);
 		P(dl.deadline);
 	}
+#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT_RT)
+	P(migration_ctrl.disable_cnt);
+	P(nr_cpus_allowed);
+#endif
 #undef PN_SCHEDSTAT
 #undef P_SCHEDSTAT