linux-kernel - [PATCH v5 1/7] sched: Introduce latency-nice as a per-task attribute

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Date:   Sun, 25 Sep 2022 16:39:02 +0200
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, bristot@...hat.com, vschneid@...hat.com,
        linux-kernel@...r.kernel.org, parth@...ux.ibm.com
Cc:     qais.yousef@....com, chris.hyser@...cle.com,
        valentin.schneider@....com, patrick.bellasi@...bug.net,
        David.Laight@...lab.com, pjt@...gle.com, pavel@....cz,
        tj@...nel.org, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v5 1/7] sched: Introduce latency-nice as a per-task attribute

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

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>
[rebase]
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 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 15e3bd96e4ce..6805f378a9c3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -783,6 +783,7 @@ struct task_struct {
 	int				static_prio;
 	int				normal_prio;
 	unsigned int			rt_priority;
+	int				latency_nice;
 
 	struct sched_entity		se;
 	struct sched_rt_entity		rt;
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index bb3d63bdf4ae..a3f7876217a6 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1042,6 +1042,7 @@ 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 1fc198be1ffd..eeb6efb0b610 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -125,6 +125,24 @@ extern int sched_rr_timeslice;
  */
 #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
-- 
2.17.1