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[PATCH] sched/core: Remove unnecessary initialization init_idle_bootup_task()

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init_idle_bootup_task( ) is called in rest_init( ) to switch
the scheduling class of the boot thread to the idle class

the function only set :
    idle->sched_class = &idle_sched_class;
which has been set in init_idle() called by sched_init()
    /*
     * The idle tasks have their own, simple scheduling class:
     */
    idle->sched_class = &idle_sched_class;

We've already set the boot thread to idle class in
start_kernel()->sched_init()->init_idle()
so it's unnecessary to set it again in
start_kernel()->rest_init()->init_idle_bootup_task()

Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>
---
 include/linux/sched/task.h | 1 -
 init/main.c                | 1 -
 kernel/sched/core.c        | 5 -----
 3 files changed, 7 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index c97e5f0..79a2a74 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -30,7 +30,6 @@
 
 extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
-extern void init_idle_bootup_task(struct task_struct *idle);
 
 extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
 extern void sched_dead(struct task_struct *p);
diff --git a/init/main.c b/init/main.c
index 052481f..881d624 100644
--- a/init/main.c
+++ b/init/main.c
@@ -430,7 +430,6 @@ static noinline void __ref rest_init(void)
 	 * The boot idle thread must execute schedule()
 	 * at least once to get things moving:
 	 */
-	init_idle_bootup_task(current);
 	schedule_preempt_disabled();
 	/* Call into cpu_idle with preempt disabled */
 	cpu_startup_entry(CPUHP_ONLINE);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0869b20..7377cac 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5177,11 +5177,6 @@ void show_state_filter(unsigned long state_filter)
 		debug_show_all_locks();
 }
 
-void init_idle_bootup_task(struct task_struct *idle)
-{
-	idle->sched_class = &idle_sched_class;
-}
-
 /**
  * init_idle - set up an idle thread for a given CPU
  * @idle: task in question
-- 
1.8.3.1

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[PATCH] sched/core: Remove unnecessary initialization init_idle_bootup_task() Cheng Jian <cj.chengjian@huawei.com> - 2017-08-04 11:20 +0200
  Re: [PATCH] sched/core: Remove unnecessary initialization  init_idle_bootup_task() Peter Zijlstra <peterz@infradead.org> - 2017-08-04 11:50 +0200
  [tip:sched/core] sched/core: Remove unnecessary initialization  init_idle_bootup_task() tip-bot for Cheng Jian <tipbot@zytor.com> - 2017-08-10 14:20 +0200

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