[RFC PATCH 1/2] sched/wait: Add wait_threshold

["Pavel Begunkov (Silence)" <asml.silence@gmail.com>]

From: Pavel Begunkov <asml.silence@gmail.com>

Add wait_threshold -- a custom wait_event derivative, that waits until
a value is equal to or greater than the specified threshold.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/wait_threshold.h | 64 ++++++++++++++++++++++++++++++++++
 kernel/sched/Makefile          |  2 +-
 kernel/sched/wait_threshold.c  | 26 ++++++++++++++
 3 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/wait_threshold.h
 create mode 100644 kernel/sched/wait_threshold.c

diff --git a/include/linux/wait_threshold.h b/include/linux/wait_threshold.h
new file mode 100644
index 000000000000..01798c3aae1f
--- /dev/null
+++ b/include/linux/wait_threshold.h
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_WAIT_THRESHOLD_H
+#define _LINUX_WAIT_THRESHOLD_H
+
+#include <linux/wait.h>
+
+struct wait_threshold_queue_entry {
+	struct wait_queue_entry wq_entry;
+	unsigned int threshold;
+};
+
+void init_wait_threshold_entry(struct wait_threshold_queue_entry *wtq_entry,
+				unsigned int threshold);
+
+static inline void wake_up_threshold(struct wait_queue_head *wq_head,
+					unsigned int val)
+{
+	void *arg = (void *)(unsigned long)val;
+
+	__wake_up(wq_head, TASK_NORMAL, 1, arg);
+}
+
+#define ___wait_threshold_event(q, thresh, condition, state,		\
+				exclusive, ret, cmd)			\
+({									\
+	__label__ __out;						\
+	struct wait_queue_head *__wq_head = &q;				\
+	struct wait_threshold_queue_entry __wtq_entry;			\
+	struct wait_queue_entry *__wq_entry = &__wtq_entry.wq_entry;	\
+	long __ret = ret; /* explicit shadow */				\
+									\
+	init_wait_threshold_entry(&__wtq_entry, thresh);		\
+	for (;;) {							\
+		long __int = prepare_to_wait_event(__wq_head,		\
+						   __wq_entry,		\
+						   state);		\
+		if (condition)						\
+			break;						\
+									\
+		if (___wait_is_interruptible(state) && __int) {		\
+			__ret = __int;					\
+			goto __out;					\
+		}							\
+									\
+		cmd;							\
+	}								\
+	finish_wait(__wq_head, __wq_entry);				\
+__out:	__ret;								\
+})
+
+#define __wait_threshold_interruptible(q, thresh, condition)		\
+	___wait_threshold_event(q, thresh, condition, TASK_INTERRUPTIBLE, 0, 0,\
+			  schedule())
+
+#define wait_threshold_interruptible(q, threshold, val)		\
+({								\
+	int __ret = 0;						\
+	might_sleep();						\
+	if ((val) < (threshold))				\
+		__ret = __wait_threshold_interruptible(q,	\
+			threshold, ((val) >= (threshold)));	\
+	__ret;							\
+})
+#endif /* _LINUX_WAIT_THRESHOLD_H */
diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile
index 21fb5a5662b5..bb895a3184f9 100644
--- a/kernel/sched/Makefile
+++ b/kernel/sched/Makefile
@@ -18,7 +18,7 @@ endif
 
 obj-y += core.o loadavg.o clock.o cputime.o
 obj-y += idle.o fair.o rt.o deadline.o
-obj-y += wait.o wait_bit.o swait.o completion.o
+obj-y += wait.o wait_bit.o wait_threshold.o swait.o completion.o
 
 obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o pelt.o
 obj-$(CONFIG_SCHED_AUTOGROUP) += autogroup.o
diff --git a/kernel/sched/wait_threshold.c b/kernel/sched/wait_threshold.c
new file mode 100644
index 000000000000..80a027c02ff3
--- /dev/null
+++ b/kernel/sched/wait_threshold.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include "sched.h"
+#include <linux/wait_threshold.h>
+
+static int wake_threshold_function(struct wait_queue_entry *wq_entry,
+				   unsigned int mode, int sync, void *arg)
+{
+	unsigned int val = (unsigned int)(unsigned long)arg;
+	struct wait_threshold_queue_entry *wtq_entry =
+		container_of(wq_entry, struct wait_threshold_queue_entry,
+			wq_entry);
+
+	if (val < wtq_entry->threshold)
+		return 0;
+
+	return default_wake_function(wq_entry, mode, sync, arg);
+}
+
+void init_wait_threshold_entry(struct wait_threshold_queue_entry *wtq_entry,
+			       unsigned int threshold)
+{
+	init_wait_entry(&wtq_entry->wq_entry, 0);
+	wtq_entry->wq_entry.func = wake_threshold_function;
+	wtq_entry->threshold = threshold;
+}
+EXPORT_SYMBOL(init_wait_threshold_entry);
-- 
2.22.0