linux-kernel - [PATCH 2/6] sched/core: Propagate parent task's latency requirements to the child task

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Message-Id: <20220311161406.23497-3-vincent.guittot@linaro.org>
Date:   Fri, 11 Mar 2022 17:14:02 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, linux-kernel@...r.kernel.org, parth@...ux.ibm.com
Cc:     qais.yousef@....com, chris.hyser@...cle.com,
        pkondeti@...eaurora.org, valentin.schneider@....com,
        patrick.bellasi@...bug.net, David.Laight@...lab.com,
        pjt@...gle.com, pavel@....cz, tj@...nel.org,
        dhaval.giani@...cle.com, qperret@...gle.com,
        tim.c.chen@...ux.intel.com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 2/6] sched/core: Propagate parent task's latency requirements to the child task

From: Parth Shah <parth@...ux.ibm.com>

Clone parent task's latency_nice attribute to the forked child task.

Reset the latency_nice value to default value when the child task is
set to sched_reset_on_fork.

Also, initialize init_task.latency_nice value with DEFAULT_LATENCY_NICE
value

Signed-off-by: Parth Shah <parth@...ux.ibm.com>
[rebase]
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 init/init_task.c    | 1 +
 kernel/sched/core.c | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/init/init_task.c b/init/init_task.c
index 73cc8f03511a..2afa249c253b 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -78,6 +78,7 @@ struct task_struct init_task
 	.prio		= MAX_PRIO - 20,
 	.static_prio	= MAX_PRIO - 20,
 	.normal_prio	= MAX_PRIO - 20,
+	.latency_nice	= 0,
 	.policy		= SCHED_NORMAL,
 	.cpus_ptr	= &init_task.cpus_mask,
 	.user_cpus_ptr	= NULL,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1d863d7f6ad7..157eef880d1d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4393,6 +4393,9 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	 */
 	p->prio = current->normal_prio;
 
+	/* Propagate the parent's latency requirements to the child as well */
+	p->latency_nice = current->latency_nice;
+
 	uclamp_fork(p);
 
 	/*
@@ -4409,6 +4412,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 		p->prio = p->normal_prio = p->static_prio;
 		set_load_weight(p, false);
 
+		p->latency_nice = DEFAULT_LATENCY_NICE;
 		/*
 		 * We don't need the reset flag anymore after the fork. It has
 		 * fulfilled its duty:
-- 
2.17.1