[PATCH V7 07/11] sched: Add API to indicate not to delay scheduling

[Prakash Sangappa]

Add an API for user threads to request scheduler to not delay
scheduling it when woken up to run. This is allowed only for RT threads.

Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
---
 include/linux/sched.h      |  1 +
 include/uapi/linux/prctl.h |  3 +++
 kernel/sys.c               | 18 ++++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5c5868c555f0..3e8eb64658d1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1062,6 +1062,7 @@ struct task_struct {
 #endif
 	unsigned			in_nf_duplicate:1;
 	unsigned			rseq_delay_resched:2;
+	unsigned			sched_nodelay:1;
 #ifdef CONFIG_PREEMPT_RT
 	struct netdev_xmit		net_xmit;
 #endif
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 6f9912c65595..907300cd4469 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -379,4 +379,7 @@ struct prctl_mm_map {
 # define PR_FUTEX_HASH_GET_SLOTS	2
 # define PR_FUTEX_HASH_GET_IMMUTABLE	3
 
+/* TASK sched nodelay request */
+#define PR_SET_SCHED_NODELAY		79
+#define PR_GET_SCHED_NODELAY		80
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index a088a6b1ac23..2f8b4512c6e4 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2890,6 +2890,24 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_FUTEX_HASH:
 		error = futex_hash_prctl(arg2, arg3, arg4);
 		break;
+	case PR_SET_SCHED_NODELAY:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		if (current->sched_class != &rt_sched_class)
+			return -EINVAL;
+		if (arg2)
+			current->sched_nodelay = 1;
+		else
+			current->sched_nodelay = 0;
+		break;
+	case PR_GET_SCHED_NODELAY:
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+		if (current->sched_class != &rt_sched_class)
+			return -EINVAL;
+		error = (current->sched_nodelay == 1);
+		break;
+
 	default:
 		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
 		error = -EINVAL;
-- 
2.43.5