Commit a09a689a authored Feb 02, 2021 by Ben Gardon Committed by Paolo Bonzini Feb 04, 2021

sched: Add needbreak for rwlocks



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@redhat.com>
CC: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Waiman Long <longman@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-8-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 26128cb6

include/linux/sched.h

+17 −0

Original line number	Diff line number	Diff line
		@@ -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());