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Date: Mon, 5 Sep 2016 14:20:03 +0800 From: cheng chao <chengchao@...acom.com> To: mingo@...nel.org, oleg@...hat.com, peterz@...radead.org, tj@...nel.org, akpm@...ux-foundation.org, chris@...is-wilson.co.uk Cc: linux-kernel@...r.kernel.org, cheng chao <chengchao@...acom.com> Subject: [PATCH] sched/core: simpler function for sched_exec migration when sched_exec needs migration and CONFIG_PREEMPT_NONE=y, migration_cpu_stop almost does nothing due to the caller is !task_on_rq_queued(). currently CONFIG_PREEMPT and CONFIG_PREEMPT_VOLUNTARY work well because the caller keeps task_on_rq_queued(): 1. when CONFIG_PREEMPT=y stop_one_cpu ->cpu_stop_queue_work ->spin_unlock_irqrestore (preempt_enable calls __preempt_schedule) 2. when CONFIG_PREEMPT_VOLUNTARY=y stop_one_cpu ->wait_for_completion ->... -->might_sleep() (calls _cond_resched() stop_one_cpu_sync is introduced here to address this problem,more further it makes more simpler for CONFIG_PREEMPT=y or CONFIG_PREEMPT_VOLUNTARY=y when sched_exec needs migration. Signed-off-by: cheng chao <chengchao@...acom.com> --- include/linux/stop_machine.h | 1 + kernel/sched/core.c | 2 +- kernel/stop_machine.c | 21 +++++++++++++++++++++ 3 files changed, 23 insertions(+), 1 deletion(-) diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h index 3cc9632..e4e7d42 100644 --- a/include/linux/stop_machine.h +++ b/include/linux/stop_machine.h @@ -28,6 +28,7 @@ struct cpu_stop_work { }; int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg); +void stop_one_cpu_sync(unsigned int cpu, cpu_stop_fn_t fn, void *arg); int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg); bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, struct cpu_stop_work *work_buf); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 556cb07..2fd71e6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2958,7 +2958,7 @@ void sched_exec(void) struct migration_arg arg = { p, dest_cpu }; raw_spin_unlock_irqrestore(&p->pi_lock, flags); - stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg); + stop_one_cpu_sync(task_cpu(p), migration_cpu_stop, &arg); return; } unlock: diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 4a1ca5f..24f8637 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -130,6 +130,27 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) return done.ret; } +/** + * the caller keeps task_on_rq_queued, so it's more suitable for + * sched_exec on the case when needs migration + */ +void stop_one_cpu_sync(unsigned int cpu, cpu_stop_fn_t fn, void *arg) +{ + struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = NULL }; + + if (!cpu_stop_queue_work(cpu, &work)) + return; + +#if defined(CONFIG_PREEMPT_NONE) || defined(CONFIG_PREEMPT_VOLUNTARY) + /* + * CONFIG_PREEMPT doesn't need call schedule here, because + * preempt_enable already does the similar thing when call + * cpu_stop_queue_work + */ + schedule(); +#endif +} + /* This controls the threads on each CPU. */ enum multi_stop_state { /* Dummy starting state for thread. */ -- 2.4.11
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