Commit 4df714be authored Oct 12, 2017 by Will Deacon Committed by Ingo Molnar Oct 25, 2017

locking/atomic: Add atomic_cond_read_acquire()



smp_cond_load_acquire() provides a way to spin on a variable with acquire
semantics until some conditional expression involving the variable is
satisfied. Architectures such as arm64 can potentially enter a low-power
state, waking up only when the value of the variable changes, which
reduces the system impact of tight polling loops.

This patch makes the same interface available to users of atomic_t,
atomic64_t and atomic_long_t, rather than require messy accesses to the
structure internals.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-3-git-send-email-will.deacon@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent e0d02285

include/asm-generic/atomic-long.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -243,4 +243,7 @@ static inline long atomic_long_add_unless(atomic_long_t *l, long a, long u)
		#define atomic_long_inc_not_zero(l) \
		ATOMIC_LONG_PFX(_inc_not_zero)((ATOMIC_LONG_PFX(_t) *)(l))

		#define atomic_long_cond_read_acquire(v, c) \
		ATOMIC_LONG_PFX(_cond_read_acquire)((ATOMIC_LONG_PFX(_t) *)(v), (c))

		#endif /* _ASM_GENERIC_ATOMIC_LONG_H */

include/linux/atomic.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -653,6 +653,8 @@ static inline int atomic_dec_if_positive(atomic_t *v)
		}
		#endif

		#define atomic_cond_read_acquire(v, c) smp_cond_load_acquire(&(v)->counter, (c))

		#ifdef CONFIG_GENERIC_ATOMIC64
		#include <asm-generic/atomic64.h>
		#endif
		@@ -1072,6 +1074,8 @@ static inline long long atomic64_fetch_andnot_release(long long i, atomic64_t *v
		}
		#endif

		#define atomic64_cond_read_acquire(v, c) smp_cond_load_acquire(&(v)->counter, (c))

		#include <asm-generic/atomic-long.h>

		#endif /* _LINUX_ATOMIC_H */

Admin message