Contention awareness while holding a spin lock is essential for reducing
latency when long running kernel operations can hold that lock. Add the
same contention detection interface for read/write spin locks.
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Will Deacon <will@xxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
---
include/linux/sched.h | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6e3a5eeec509..5d1378e5a040 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1912,6 +1912,23 @@ static inline int spin_needbreak(spinlock_t *lock)
#endif
}
+/*
+ * Check if a rwlock is contended.
+ * Returns non-zero if there is another task waiting on the rwlock.
+ * Returns zero if the lock is not contended or the system / underlying
+ * rwlock implementation does not support contention detection.
+ * Technically does not depend on CONFIG_PREEMPTION, but a general need
+ * for low latency.
+ */
+static inline int rwlock_needbreak(rwlock_t *lock)
+{
+#ifdef CONFIG_PREEMPTION
+ return rwlock_is_contended(lock);
+#else
+ return 0;
+#endif
+}
+
static __always_inline bool need_resched(void)
{
return unlikely(tif_need_resched());
--
2.30.0.365.g02bc693789-goog
