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Message-Id: <20230731023308.3748432-1-guoren@kernel.org>
Date: Sun, 30 Jul 2023 22:33:08 -0400
From: guoren@...nel.org
To: guoren@...nel.org, David.Laight@...LAB.COM, will@...nel.org,
peterz@...radead.org, mingo@...hat.com, longman@...hat.com
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH V2] asm-generic: ticket-lock: Optimize arch_spin_value_unlocked
From: Guo Ren <guoren@...ux.alibaba.com>
The arch_spin_value_unlocked would cause an unnecessary memory
access to the contended value. Although it won't cause a significant
performance gap in most architectures, the arch_spin_value_unlocked
argument contains enough information. Thus, remove unnecessary
atomic_read in arch_spin_value_unlocked().
The caller of arch_spin_value_unlocked() could benefit from this
change. Currently, the only caller is lockref.
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: David Laight <David.Laight@...LAB.COM>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
---
Changelog
V2:
- Fixup commit log with Waiman advice.
- Add Waiman comment in the commit msg.
---
include/asm-generic/spinlock.h | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h
index fdfebcb050f4..90803a826ba0 100644
--- a/include/asm-generic/spinlock.h
+++ b/include/asm-generic/spinlock.h
@@ -68,11 +68,18 @@ static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
smp_store_release(ptr, (u16)val + 1);
}
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+ u32 val = lock.counter;
+
+ return ((val >> 16) == (val & 0xffff));
+}
+
static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
- u32 val = atomic_read(lock);
+ arch_spinlock_t val = READ_ONCE(*lock);
- return ((val >> 16) != (val & 0xffff));
+ return !arch_spin_value_unlocked(val);
}
static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
@@ -82,11 +89,6 @@ static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
return (s16)((val >> 16) - (val & 0xffff)) > 1;
}
-static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
- return !arch_spin_is_locked(&lock);
-}
-
#include <asm/qrwlock.h>
#endif /* __ASM_GENERIC_SPINLOCK_H */
--
2.36.1
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