linux-kernel - [PATCH] sched/fair: Preserve PLACE_DEADLINE

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Message-ID: <20231004011737.188682-1-daniel.m.jordan@oracle.com>
Date:   Tue,  3 Oct 2023 21:17:37 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     peterz@...radead.org
Cc:     bristot@...hat.com, bsegall@...gle.com, chris.hyser@...cle.com,
        corbet@....net, dietmar.eggemann@....com, efault@....de,
        joel@...lfernandes.org, joshdon@...gle.com, juri.lelli@...hat.com,
        kprateek.nayak@....com, linux-kernel@...r.kernel.org,
        mgorman@...e.de, mingo@...nel.org, patrick.bellasi@...bug.net,
        pavel@....cz, pjt@...gle.com, qperret@...gle.com,
        qyousef@...alina.io, rostedt@...dmis.org, tglx@...utronix.de,
        tim.c.chen@...ux.intel.com, timj@....org,
        vincent.guittot@...aro.org, youssefesmat@...omium.org,
        yu.c.chen@...el.com, daniel.m.jordan@...cle.com
Subject: [PATCH] sched/fair: Preserve PLACE_DEADLINE_INITIAL deadline

An entity is supposed to get an earlier deadline with
PLACE_DEADLINE_INITIAL when it's forked, but the deadline gets
overwritten soon after in enqueue_entity() the first time a forked
entity is woken so that PLACE_DEADLINE_INITIAL is effectively a no-op.

Placing in task_fork_fair() seems unnecessary since none of the values
that get set (slice, vruntime, deadline) are used before they're set
again at enqueue time, so get rid of that and just pass ENQUEUE_INITIAL
to enqueue_entity() via wake_up_new_task().

Fixes: e8f331bcc270 ("sched/smp: Use lag to simplify cross-runqueue placement")
Signed-off-by: Daniel Jordan <daniel.m.jordan@...cle.com>
---

Tested on top of peterz/sched/eevdf from 2023-10-03.

 kernel/sched/core.c | 2 +-
 kernel/sched/fair.c | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 779cdc7969c81..500e2dbfd41dd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4854,7 +4854,7 @@ void wake_up_new_task(struct task_struct *p)
 	update_rq_clock(rq);
 	post_init_entity_util_avg(p);
 
-	activate_task(rq, p, ENQUEUE_NOCLOCK);
+	activate_task(rq, p, ENQUEUE_INITIAL | ENQUEUE_NOCLOCK);
 	trace_sched_wakeup_new(p);
 	wakeup_preempt(rq, p, WF_FORK);
 #ifdef CONFIG_SMP
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a0b4dac2662c9..5872b8a3f5891 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12446,7 +12446,6 @@ static void task_fork_fair(struct task_struct *p)
 	curr = cfs_rq->curr;
 	if (curr)
 		update_curr(cfs_rq);
-	place_entity(cfs_rq, se, ENQUEUE_INITIAL);
 	rq_unlock(rq, &rf);
 }
 
-- 
2.41.0