[PATCH v14 11/15] sched: add need-resched timed wait interface

Add tif_bitset_relaxed_wait() (and tif_need_resched_relaxed_wait()
which wraps it) which takes the thread_info bit and timeout duration
as parameters and waits until the bit is set or for the expiration
of the timeout.

The wait is implemented via smp_cond_load_relaxed_timeout().

smp_cond_load_relaxed_timeout() essentially provides the pattern used
in poll_idle() where we spin in a loop waiting for the flag to change
until a timeout occurs.

tif_need_resched_relaxed_wait() allows us to abstract out the internals
of waiting, scheduler specific details etc.

Placed in linux/sched/idle.h instead of linux/thread_info.h to work
around recursive include hell.

Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Daniel Lezcano <[email protected]>
Cc: [email protected]
Signed-off-by: Ankur Arora <[email protected]>
---
 include/linux/sched/idle.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/sched/idle.h b/include/linux/sched/idle.h
index 8465ff1f20d1..ddee9b019895 100644
--- a/include/linux/sched/idle.h
+++ b/include/linux/sched/idle.h
@@ -3,6 +3,7 @@
 #define _LINUX_SCHED_IDLE_H
 
 #include <linux/sched.h>
+#include <linux/sched/clock.h>
 
 enum cpu_idle_type {
 	__CPU_NOT_IDLE = 0,
@@ -113,4 +114,32 @@ static __always_inline void current_clr_polling(void)
 }
 #endif
 
+/*
+ * Caller needs to make sure that the thread context cannot be preempted
+ * or migrated, so current_thread_info() cannot change from under us.
+ *
+ * This also allows us to safely stay in the local_clock domain.
+ */
+static __always_inline bool tif_bitset_relaxed_wait(int tif, u64 timeout_ns)
+{
+	unsigned long flags;
+
+	flags = smp_cond_load_relaxed_timeout(&current_thread_info()->flags,
+					      (VAL & BIT(tif)),
+					      local_clock_noinstr(),
+					      timeout_ns);
+	return flags & BIT(tif);
+}
+
+/**
+ * tif_need_resched_relaxed_wait() - Wait for need-resched being set
+ * with no ordering guarantees until a timeout expires.
+ *
+ * @timeout_ns: timeout value.
+ */
+static __always_inline bool tif_need_resched_relaxed_wait(u64 timeout_ns)
+{
+	return tif_bitset_relaxed_wait(TIF_NEED_RESCHED, timeout_ns);
+}
+
 #endif /* _LINUX_SCHED_IDLE_H */
-- 
2.43.7