From: Cheng Chao <cs.os.kernel@gmail.com>
To: mingo@kernel.org, oleg@redhat.com, peterz@infradead.org,
tj@kernel.org, akpm@linux-foundation.org,
chris@chris-wilson.co.uk
Cc: linux-kernel@vger.kernel.org, Cheng Chao <cs.os.kernel@gmail.com>
Subject: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE
Date: Sat, 10 Sep 2016 16:52:12 +0800 [thread overview]
Message-ID: <1473497532-5440-1-git-send-email-cs.os.kernel@gmail.com> (raw)
In-Reply-To: <1473408834-6122-1-git-send-email-chengchao@kedacom.com>
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;
}
--
2.4.11
next prev parent reply other threads:[~2016-09-10 8:52 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <OF73BCE1E4.D2224FEC-ON48258025.0022CFA7-48258025.0022E3DC@kedacom.com>
2016-09-09 8:13 ` [PATCH v2] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao
2016-09-09 8:19 ` chengchao
2016-09-09 13:14 ` Oleg Nesterov
2016-09-09 16:24 ` Peter Zijlstra
2016-09-10 8:52 ` Cheng Chao [this message]
2016-09-10 9:51 ` [PATCH v3] " Cheng Chao
2016-09-10 16:33 ` Peter Zijlstra
2016-09-12 11:03 ` Oleg Nesterov
2016-09-13 2:45 ` Cheng Chao
2016-09-12 11:37 ` Peter Zijlstra
2016-09-12 11:41 ` Peter Zijlstra
2016-09-12 13:05 ` Oleg Nesterov
2016-09-12 15:01 ` Peter Zijlstra
2016-09-13 16:14 ` Oleg Nesterov
2016-09-13 16:37 ` Peter Zijlstra
2016-09-14 2:07 ` Cheng Chao
2016-09-14 7:50 ` Peter Zijlstra
2016-09-14 15:45 ` Oleg Nesterov
2016-09-22 13:59 ` [tip:sched/core] sched/core: Optimize __schedule() tip-bot for Peter Zijlstra
2016-09-13 4:03 ` [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE Cheng Chao
2016-09-13 8:45 ` Peter Zijlstra
2016-09-14 2:01 ` [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() Cheng Chao
2016-09-14 15:53 ` Oleg Nesterov
2016-09-18 2:07 ` Cheng Chao
2016-09-22 13:59 ` [tip:sched/core] stop_machine: Avoid a sleep and wakeup in stop_one_cpu() tip-bot for Cheng Chao
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