linux-kernel - [PATCH sched_ext/for-6.11] sched_ext: Account for idle policy when setting p->scx.weight in scx_ops_enable

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Date: Tue, 25 Jun 2024 16:19:28 -1000
From: Tejun Heo <tj@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: torvalds@...ux-foundation.org, mingo@...hat.com, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
	bristot@...hat.com, vschneid@...hat.com, ast@...nel.org,
	daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
	joshdon@...gle.com, brho@...gle.com, pjt@...gle.com,
	derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com,
	dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com,
	changwoo@...lia.com, himadrics@...ia.fr, memxor@...il.com,
	andrea.righi@...onical.com, joel@...lfernandes.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	kernel-team@...a.com
Subject: [PATCH sched_ext/for-6.11] sched_ext: Account for idle policy when
 setting p->scx.weight in scx_ops_enable_task()

When initializing p->scx.weight, scx_ops_enable_task() wasn't considering
whether the task is SCHED_IDLE. Update it to use WEIGHT_IDLEPRIO as the
source weight for SCHED_IDLE tasks. This leaves reweight_task_scx() the sole
user of set_task_scx_weight(). Open code it. @weight is going to be provided
by sched core in the future anyway.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
This is a related fix for sched_ext.

Thanks.

 kernel/sched/ext.c |   21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3237,22 +3237,23 @@ static int scx_ops_init_task(struct task
 	return 0;
 }
 
-static void set_task_scx_weight(struct task_struct *p)
-{
-	u32 weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO];
-
-	p->scx.weight = sched_weight_to_cgroup(weight);
-}
-
 static void scx_ops_enable_task(struct task_struct *p)
 {
+	u32 weight;
+
 	lockdep_assert_rq_held(task_rq(p));
 
 	/*
 	 * Set the weight before calling ops.enable() so that the scheduler
 	 * doesn't see a stale value if they inspect the task struct.
 	 */
-	set_task_scx_weight(p);
+	if (task_has_idle_policy(p))
+		weight = WEIGHT_IDLEPRIO;
+	else
+		weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO];
+
+	p->scx.weight = sched_weight_to_cgroup(weight);
+
 	if (SCX_HAS_OP(enable))
 		SCX_CALL_OP_TASK(SCX_KF_REST, enable, p);
 	scx_set_task_state(p, SCX_TASK_ENABLED);
@@ -3405,9 +3406,11 @@ void sched_ext_free(struct task_struct *
 
 static void reweight_task_scx(struct rq *rq, struct task_struct *p, int newprio)
 {
+	unsigned long weight = sched_prio_to_weight[newprio];
+
 	lockdep_assert_rq_held(task_rq(p));
 
-	set_task_scx_weight(p);
+	p->scx.weight = sched_weight_to_cgroup(weight);
 	if (SCX_HAS_OP(set_weight))
 		SCX_CALL_OP_TASK(SCX_KF_REST, set_weight, p, p->scx.weight);
 }