lkml.org 
[lkml]   [2016]   [Sep]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu()
Date
In case @cpu == smp_proccessor_id(), we can avoid a sleep+wakeup
by doing a preemption.

the caller such as sched_exec can benefit from this change.

Signed-off-by: Cheng Chao <cs.os.kernel@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
kernel/sched/core.c | 8 ++++++--
kernel/stop_machine.c | 5 +++++
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a0086a5..283b662 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1063,8 +1063,12 @@ static int migration_cpu_stop(void *data)
* holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
* we're holding p->pi_lock.
*/
- if (task_rq(p) == rq && task_on_rq_queued(p))
- rq = __migrate_task(rq, p, arg->dest_cpu);
+ if (task_rq(p) == rq) {
+ if (task_on_rq_queued(p))
+ rq = __migrate_task(rq, p, arg->dest_cpu);
+ else
+ p->wake_cpu = arg->dest_cpu;
+ }
raw_spin_unlock(&rq->lock);
raw_spin_unlock(&p->pi_lock);

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 4a1ca5f..1a24890 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -126,6 +126,11 @@ 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;
+ /*
+ * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
+ * by doing a preemption.
+ */
+ cond_resched();
wait_for_completion(&done.completion);
return done.ret;
}
--
2.4.11
\
 
 \ /
  Last update: 2016-09-17 09:59    [W:0.122 / U:0.488 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site