[RFC v4 1/8] sched/core: Add manual jitter classification using sched_setattr syscall

[Parth Shah <parth@linux.ibm.com>]

Jitter tasks are short/bursty tasks, typically performing some housekeeping
work and are less important in the overall scheme of things.

So provide a way to mark the task as jitter with the use of additional flag
to the existing task attribute. Also provide an interface from the
userspace which uses sched_setattr syscall to mark tasks as jitter.

Signed-off-by: Parth Shah <parth@linux.ibm.com>
---
 include/linux/sched.h      | 1 +
 include/uapi/linux/sched.h | 4 +++-
 kernel/sched/core.c        | 9 +++++++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1113dd4706ae..e03b85166e34 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1463,6 +1463,7 @@ extern struct pid *cad_pid;
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_NOCMA	0x10000000	/* All allocation request will have _GFP_MOVABLE cleared */
+#define PF_CAN_BE_PACKED	0x20000000	/* Provide hints to the scheduler to pack such tasks */
 #define PF_FREEZER_SKIP		0x40000000	/* Freezer should not count it as freezable */
 #define PF_SUSPEND_TASK		0x80000000      /* This thread called freeze_processes() and should not be frozen */
 
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 617bb59aa8ba..fccb1c57d037 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -55,6 +55,7 @@
 #define SCHED_FLAG_KEEP_PARAMS		0x10
 #define SCHED_FLAG_UTIL_CLAMP_MIN	0x20
 #define SCHED_FLAG_UTIL_CLAMP_MAX	0x40
+#define SCHED_FLAG_TASK_PACKING		0x80
 
 #define SCHED_FLAG_KEEP_ALL	(SCHED_FLAG_KEEP_POLICY | \
 				 SCHED_FLAG_KEEP_PARAMS)
@@ -66,6 +67,7 @@
 			 SCHED_FLAG_RECLAIM		| \
 			 SCHED_FLAG_DL_OVERRUN		| \
 			 SCHED_FLAG_KEEP_ALL		| \
-			 SCHED_FLAG_UTIL_CLAMP)
+			 SCHED_FLAG_UTIL_CLAMP		| \
+			 SCHED_FLAG_TASK_PACKING)
 
 #endif /* _UAPI_LINUX_SCHED_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fa43ce3962e7..e7cda4aa8696 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4498,6 +4498,8 @@ 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);
+	if (attr->sched_flags & SCHED_FLAG_TASK_PACKING)
+		p->flags |= PF_CAN_BE_PACKED;
 }
 
 /* Actually do priority change: must hold pi & rq lock. */
@@ -4557,6 +4559,8 @@ static int __sched_setscheduler(struct task_struct *p,
 	struct rq_flags rf;
 	int reset_on_fork;
 	int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
+	unsigned long long task_packing_flag =
+				attr->sched_flags & SCHED_FLAG_TASK_PACKING;
 	struct rq *rq;
 
 	/* The pi code expects interrupts enabled */
@@ -4686,6 +4690,8 @@ static int __sched_setscheduler(struct task_struct *p,
 			goto change;
 		if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
 			goto change;
+		if (task_packing_flag)
+			goto change;
 
 		p->sched_reset_on_fork = reset_on_fork;
 		task_rq_unlock(rq, p, &rf);
@@ -5181,6 +5187,9 @@ SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
 	attr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
 #endif
 
+	if (p->flags & PF_CAN_BE_PACKED)
+		attr.sched_flags |= SCHED_FLAG_TASK_PACKING;
+
 	rcu_read_unlock();
 
 	retval = sched_read_attr(uattr, &attr, size);
-- 
2.17.1