Messages in this thread Patch in this message | | | From | Chengming Zhou <> | Subject | [PATCH v4] sched/core: Minor optimize ttwu_runnable() | Date | Fri, 2 Dec 2022 16:06:44 +0800 |
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ttwu_runnable() is used as a fast wakeup path when the wakee task is running on CPU or runnable on RQ, in both cases we can just set its state to TASK_RUNNING to prevent a sleep.
If the wakee task is on_cpu running, we don't need to update_rq_clock() or check_preempt_curr().
But if the wakee task is on_rq && !on_cpu (e.g. an IRQ hit before the task got to schedule() and the task been preempted), we should check_preempt_curr() to see if it can preempt the current running.
Reorganize ttwu_do_wakeup() and ttwu_do_activate() to make ttwu_do_wakeup() only mark the task runnable, so it can be used in ttwu_runnable() and try_to_wake_up() fast paths.
This also removes the class->task_woken() callback from ttwu_runnable(), which wasn't required per the RT/DL implementations: any required push operation would have been queued during class->set_next_task() when p got preempted.
ttwu_runnable() also loses the update to rq->idle_stamp, as by definition the rq cannot be idle in this scenario.
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Suggested-by: Valentin Schneider <vschneid@redhat.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> --- v4: - s/This patch reorg/Reorganize/ per Bagas Sanjaya. Thanks!
v3: - Improve the changelog per Valentin Schneider. Thanks!
v2: - keep check_preempt_curr() for on_rq && !on_cpu case in ttwu_runnable(), per Valentin Schneider. - reorg ttwu_do_wakeup() and ttwu_do_activate() code, so ttwu_do_wakeup() can be reused in ttwu_runnable(), per Peter Zijlstra. - reuse ttwu_do_wakeup() in try_to_wake_up() (p == current) fast path too, so ttwu_do_wakeup() become the only place we mark task runnable. --- kernel/sched/core.c | 73 ++++++++++++++++++++++++--------------------- 1 file changed, 39 insertions(+), 34 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 314c2c0219d9..d8216485b0ad 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3623,14 +3623,39 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags) } /* - * Mark the task runnable and perform wakeup-preemption. + * Mark the task runnable. */ -static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags, - struct rq_flags *rf) +static inline void ttwu_do_wakeup(struct task_struct *p) { - check_preempt_curr(rq, p, wake_flags); WRITE_ONCE(p->__state, TASK_RUNNING); trace_sched_wakeup(p); +} + +static void +ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags, + struct rq_flags *rf) +{ + int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK; + + lockdep_assert_rq_held(rq); + + if (p->sched_contributes_to_load) + rq->nr_uninterruptible--; + +#ifdef CONFIG_SMP + if (wake_flags & WF_MIGRATED) + en_flags |= ENQUEUE_MIGRATED; + else +#endif + if (p->in_iowait) { + delayacct_blkio_end(p); + atomic_dec(&task_rq(p)->nr_iowait); + } + + activate_task(rq, p, en_flags); + check_preempt_curr(rq, p, wake_flags); + + ttwu_do_wakeup(p); #ifdef CONFIG_SMP if (p->sched_class->task_woken) { @@ -3660,31 +3685,6 @@ static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags, #endif } -static void -ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags, - struct rq_flags *rf) -{ - int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK; - - lockdep_assert_rq_held(rq); - - if (p->sched_contributes_to_load) - rq->nr_uninterruptible--; - -#ifdef CONFIG_SMP - if (wake_flags & WF_MIGRATED) - en_flags |= ENQUEUE_MIGRATED; - else -#endif - if (p->in_iowait) { - delayacct_blkio_end(p); - atomic_dec(&task_rq(p)->nr_iowait); - } - - activate_task(rq, p, en_flags); - ttwu_do_wakeup(rq, p, wake_flags, rf); -} - /* * Consider @p being inside a wait loop: * @@ -3718,9 +3718,15 @@ static int ttwu_runnable(struct task_struct *p, int wake_flags) rq = __task_rq_lock(p, &rf); if (task_on_rq_queued(p)) { - /* check_preempt_curr() may use rq clock */ - update_rq_clock(rq); - ttwu_do_wakeup(rq, p, wake_flags, &rf); + if (!task_on_cpu(rq, p)) { + /* + * When on_rq && !on_cpu the task is preempted, see if + * it should preempt whatever is current there now. + */ + update_rq_clock(rq); + check_preempt_curr(rq, p, wake_flags); + } + ttwu_do_wakeup(p); ret = 1; } __task_rq_unlock(rq, &rf); @@ -4086,8 +4092,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) goto out; trace_sched_waking(p); - WRITE_ONCE(p->__state, TASK_RUNNING); - trace_sched_wakeup(p); + ttwu_do_wakeup(p); goto out; } -- 2.37.2
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