Messages in this thread Patch in this message | | | From | Cheng Chao <> | Subject | [PATCH v4] stop_machine: Avoid a sleep and wakeup in the stop_one_cpu() | Date | Wed, 14 Sep 2016 10:01:50 +0800 |
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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
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