[RFC 3/3] Allow sched_{get,set}attr to change latency_tolerance of the task

[Parth Shah]

Introduce the latency_tolerance attribute to sched_attr and provide a
mechanism to change the value with the use of sched_setattr/sched_getattr
syscall.

Also add new flag "SCHED_FLAG_LATENCY_TOLERANCE" to hint the change in
latency_tolerance of the task on every sched_setattr syscall.

Signed-off-by: Parth Shah <parth@xxxxxxxxxxxxx>
---
 include/uapi/linux/sched.h       |  4 +++-
 include/uapi/linux/sched/types.h |  2 ++
 kernel/sched/core.c              | 15 +++++++++++++++
 kernel/sched/sched.h             |  1 +
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index b3105ac1381a..73db430d11b6 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -71,6 +71,7 @@ struct clone_args {
 #define SCHED_FLAG_KEEP_PARAMS		0x10
 #define SCHED_FLAG_UTIL_CLAMP_MIN	0x20
 #define SCHED_FLAG_UTIL_CLAMP_MAX	0x40
+#define SCHED_FLAG_LATENCY_TOLERANCE	0x80
 
 #define SCHED_FLAG_KEEP_ALL	(SCHED_FLAG_KEEP_POLICY | \
 				 SCHED_FLAG_KEEP_PARAMS)
@@ -82,6 +83,7 @@ struct clone_args {
 			 SCHED_FLAG_RECLAIM		| \
 			 SCHED_FLAG_DL_OVERRUN		| \
 			 SCHED_FLAG_KEEP_ALL		| \
-			 SCHED_FLAG_UTIL_CLAMP)
+			 SCHED_FLAG_UTIL_CLAMP		| \
+			 SCHED_FLAG_LATENCY_TOLERANCE)
 
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/include/uapi/linux/sched/types.h b/include/uapi/linux/sched/types.h
index c852153ddb0d..960774ac0c70 100644
--- a/include/uapi/linux/sched/types.h
+++ b/include/uapi/linux/sched/types.h
@@ -118,6 +118,8 @@ struct sched_attr {
 	__u32 sched_util_min;
 	__u32 sched_util_max;
 
+	/* latency requirement hints */
+	__s32 sched_latency_tolerance;
 };
 
 #endif /* _UAPI_LINUX_SCHED_TYPES_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ea7abbf5c1bb..dfd36ec14404 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4695,6 +4695,9 @@ static void __setscheduler_params(struct task_struct *p,
 	p->rt_priority = attr->sched_priority;
 	p->normal_prio = normal_prio(p);
 	set_load_weight(p, true);
+
+	/* Change latency tolerance of the task if !SCHED_FLAG_KEEP_PARAMS */
+	p->latency_tolerance = attr->sched_latency_tolerance;
 }
 
 /* Actually do priority change: must hold pi & rq lock. */
@@ -4852,6 +4855,13 @@ static int __sched_setscheduler(struct task_struct *p,
 			return retval;
 	}
 
+	if (attr->sched_flags & SCHED_FLAG_LATENCY_TOLERANCE) {
+		if (attr->sched_latency_tolerance > MAX_LATENCY_TOLERANCE)
+			return -EINVAL;
+		if (attr->sched_latency_tolerance < MIN_LATENCY_TOLERANCE)
+			return -EINVAL;
+	}
+
 	if (pi)
 		cpuset_read_lock();
 
@@ -4886,6 +4896,9 @@ static int __sched_setscheduler(struct task_struct *p,
 			goto change;
 		if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
 			goto change;
+		if (attr->sched_flags & SCHED_FLAG_LATENCY_TOLERANCE &&
+		    attr->sched_latency_tolerance != p->latency_tolerance)
+			goto change;
 
 		p->sched_reset_on_fork = reset_on_fork;
 		retval = 0;
@@ -5392,6 +5405,8 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	else
 		kattr.sched_nice = task_nice(p);
 
+	kattr.sched_latency_tolerance = p->latency_tolerance;
+
 #ifdef CONFIG_UCLAMP_TASK
 	kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
 	kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0db2c1b3361e..bb181175954b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -21,6 +21,7 @@
 #include <linux/sched/nohz.h>
 #include <linux/sched/numa_balancing.h>
 #include <linux/sched/prio.h>
+#include <linux/sched/latency_tolerance.h>
 #include <linux/sched/rt.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/smt.h>
-- 
2.17.2