Messages in this thread | | | Subject | Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE | From | Cheng Chao <> | Date | Sat, 10 Sep 2016 17:51:02 +0800 |
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hi Peter, I guess you can receive the mail from me now, I have changed the mailbox to gmail.
Oleg has already done much work for this patch, I am really obliged. please review this patch, thanks.
on 09/10/2016 04:52 PM, Cheng Chao wrote: > 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 <cs.os.kernel@gmail.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; > } >
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