linux-kernel - [PATCH v5 2/4] sched/core: Propagate parent task's latency requirements to the child task

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Message-Id: <20200228090755.22829-3-parth@linux.ibm.com>
Date:   Fri, 28 Feb 2020 14:37:53 +0530
From:   Parth Shah <parth@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, qais.yousef@....com,
        chris.hyser@...cle.com, pkondeti@...eaurora.org,
        patrick.bellasi@...bug.net, valentin.schneider@....com,
        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
Subject: [PATCH v5 2/4] sched/core: Propagate parent task's latency requirements to the child task

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>
Reviewed-by: Qais Yousef <qais.yousef@....com>
---
 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 9e5cbe5eab7b..0d7d865519b8 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -69,6 +69,7 @@ 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,
 	.cpus_mask	= CPU_MASK_ALL,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8e6f38073ab3..866ea3d2d284 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2847,6 +2847,9 @@ 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);
 
 	/*
@@ -2863,6 +2866,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 		p->prio = p->normal_prio = __normal_prio(p);
 		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:
-- 
2.17.2