Messages in this thread Patch in this message | | | From | Cheng Chao <> | Subject | [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE | Date | Fri, 9 Sep 2016 16:13:54 +0800 |
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For CONFIG_PREEMPT_NONE=y, when sched_exec() needs migration, sched_exec() calls stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg).
If the migration_cpu_stop() can not migrate,why do we call stop_one_cpu()? It just makes the task TASK_UNINTERRUPTIBLE, wakes up the stopper thread, executes migration_cpu_stop(), and the stopper thread wakes up the task.
But in fact, all above works are almost useless(wasteful),the reason is migration_cpu_stop() can not migrate. why? migration_cpu_stop() needs the task is TASK_ON_RQ_QUEUED before it calls __migrate_task().
This patch keeps the task TASK_RUNNING instead of TASK_UNINTERRUPTIBLE, so the migration_cpu_stop() can do useful works.
Signed-off-by: Cheng Chao <chengchao@kedacom.com> --- kernel/stop_machine.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 4a1ca5f..41aea5e 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -126,6 +126,17 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) cpu_stop_init_done(&done, 1); if (!cpu_stop_queue_work(cpu, &work)) return -ENOENT; + +#if defined(CONFIG_PREEMPT_NONE) + /* + * Makes the stopper thread run as soon as possible. + * And if the caller is TASK_RUNNING, keeps the caller TASK_RUNNING. + * It's special useful for some callers which are expected to be + * TASK_ON_RQ_QUEUED. + * sched_exec does benefit from this improvement. + */ + schedule(); +#endif wait_for_completion(&done.completion); return done.ret; } -- 2.4.11
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