Messages in this thread | | | Date | Wed, 21 Dec 2022 10:01:30 +0800 | Subject | Re: [PATCH v5 1/2] sched/core: Minor optimize ttwu_runnable() | From | Chengming Zhou <> |
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Hello, ping :-)
On 2022/12/8 11:20, Chengming Zhou wrote: > 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. > > 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> > --- > v5: > - Split the reorganization and optimization into two patches > per Chen Yu. Thanks! > > 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 | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 314c2c0219d9..60aa7774e5f4 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3718,9 +3718,16 @@ 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); > + } > + WRITE_ONCE(p->__state, TASK_RUNNING); > + trace_sched_wakeup(p); > ret = 1; > } > __task_rq_unlock(rq, &rf);
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