Commit-ID: bf89a304722f6904009499a31dc68ab9a5c9742e Gitweb: http://git.kernel.org/tip/bf89a304722f6904009499a31dc68ab9a5c9742e Author: Cheng Chao <cs.os.ker...@gmail.com> AuthorDate: Wed, 14 Sep 2016 10:01:50 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Thu, 22 Sep 2016 14:53:45 +0200
stop_machine: Avoid a sleep and wakeup in stop_one_cpu() In case @cpu == smp_proccessor_id(), we can avoid a sleep+wakeup cycle by doing a preemption. Callers such as sched_exec() can benefit from this change. Signed-off-by: Cheng Chao <cs.os.ker...@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Oleg Nesterov <o...@redhat.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: a...@linux-foundation.org Cc: ch...@chris-wilson.co.uk Cc: t...@kernel.org Link: http://lkml.kernel.org/r/1473818510-6779-1-git-send-email-cs.os.ker...@gmail.com Signed-off-by: Ingo Molnar <mi...@kernel.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 c5f020c..ff4e3c0 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..082e71f 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 + * cycle by doing a preemption: + */ + cond_resched(); wait_for_completion(&done.completion); return done.ret; }
