linux-kernel - [PATCH 01/10] sched: Introduce latency-nice as a per-task attribute

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Date:   Mon, 06 Mar 2023 14:25:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, vincent.guittot@...aro.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, corbet@....net, qyousef@...alina.io,
        chris.hyser@...cle.com, patrick.bellasi@...bug.net, pjt@...gle.com,
        pavel@....cz, qperret@...gle.com, tim.c.chen@...ux.intel.com,
        joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
        yu.c.chen@...el.com, youssefesmat@...omium.org,
        joel@...lfernandes.org, Parth Shah <parth@...ux.ibm.com>
Subject: [PATCH 01/10] 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.

[rebase, move defines in sched/prio.h]
Signed-off-by: Parth Shah <parth@...ux.ibm.com>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@....com>
Link: https://lkml.kernel.org/r/20230224093454.956298-3-vincent.guittot@linaro.org
---
 include/linux/sched.h      |  1 +
 include/linux/sched/prio.h | 18 ++++++++++++++++++
 kernel/sched/debug.c       |  1 +
 3 files changed, 20 insertions(+)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -784,6 +784,7 @@ 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;
Index: linux-2.6/include/linux/sched/prio.h
===================================================================
--- linux-2.6.orig/include/linux/sched/prio.h
+++ linux-2.6/include/linux/sched/prio.h
@@ -42,4 +42,22 @@ static inline long rlimit_to_nice(long p
 	return (MAX_NICE - prio + 1);
 }
 
+/*
+ * 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
+
 #endif /* _LINUX_SCHED_PRIO_H */
Index: linux-2.6/kernel/sched/debug.c
===================================================================
--- linux-2.6.orig/kernel/sched/debug.c
+++ linux-2.6/kernel/sched/debug.c
@@ -1043,6 +1043,7 @@ void proc_sched_show_task(struct task_st
 #endif
 	P(policy);
 	P(prio);
+	P(latency_nice);
 	if (task_has_dl_policy(p)) {
 		P(dl.runtime);
 		P(dl.deadline);