linux-kernel - [PATCH v5 1/4] sched: Introduce latency-nice as a per-task attribute

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Date:   Fri, 28 Feb 2020 14:37:52 +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 1/4] sched: Introduce latency-nice as a per-task attribute

Latency-nice indicates the latency requirements of a task with respect
to the other tasks in the system. The value of the attribute can be within
the range of [-20, 19] both inclusive to be in-line with the values just
like task nice values.

latency_nice = -20 indicates the task to have the least latency as
compared to the tasks having latency_nice = +19.

The latency_nice may affect only the CFS SCHED_CLASS by getting
latency requirements from the userspace.

Additionally, add debugging bits for newly added latency_nice attribute.

Signed-off-by: Parth Shah <parth@...ux.ibm.com>
Reviewed-by: Qais Yousef <qais.yousef@....com>
---
 include/linux/sched.h |  1 +
 kernel/sched/debug.c  |  1 +
 kernel/sched/sched.h  | 18 ++++++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2e9199bf947b..cf23c147dd36 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -679,6 +679,7 @@ struct task_struct {
 	int				static_prio;
 	int				normal_prio;
 	unsigned int			rt_priority;
+	int				latency_nice;
 
 	const struct sched_class	*sched_class;
 	struct sched_entity		se;
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8331bc04aea2..2a96dadc9752 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -958,6 +958,7 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 #endif
 	P(policy);
 	P(prio);
+	P(latency_nice);
 	if (task_has_dl_policy(p)) {
 		P(dl.runtime);
 		P(dl.deadline);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2a0caf394dd4..a857e1baebd7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -101,6 +101,24 @@ extern long calc_load_fold_active(struct rq *this_rq, long adjust);
  */
 #define NS_TO_JIFFIES(TIME)	((unsigned long)(TIME) / (NSEC_PER_SEC / HZ))
 
+/*
+ * Latency nice is meant to provide scheduler hints about the relative
+ * latency requirements of a task with respect to other tasks.
+ * Thus a task with latency_nice == 19 can be hinted as the task with no
+ * latency requirements, in contrast to the task with latency_nice == -20
+ * which should be given priority in terms of lower latency.
+ */
+#define MAX_LATENCY_NICE	19
+#define MIN_LATENCY_NICE	-20
+
+#define LATENCY_NICE_WIDTH	\
+	(MAX_LATENCY_NICE - MIN_LATENCY_NICE + 1)
+
+/*
+ * Default tasks should be treated as a task with latency_nice = 0.
+ */
+#define DEFAULT_LATENCY_NICE	0
+
 /*
  * Increase resolution of nice-level calculations for 64-bit architectures.
  * The extra resolution improves shares distribution and load balancing of
-- 
2.17.2