From: guoren@kernel.org
To: guoren@kernel.org, David.Laight@ACULAB.COM, will@kernel.org,
peterz@infradead.org, mingo@redhat.com, longman@redhat.com
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-riscv@lists.infradead.org,
Guo Ren <guoren@linux.alibaba.com>
Subject: [PATCH] asm-generic: ticket-lock: Optimize arch_spin_value_unlocked
Date: Wed, 19 Jul 2023 03:00:01 -0400 [thread overview]
Message-ID: <20230719070001.795010-1-guoren@kernel.org> (raw)
From: Guo Ren <guoren@linux.alibaba.com>
Using arch_spinlock_is_locked would cause another 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().
Signed-off-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Peter Zijlstra <peterz@infradead.org>
---
Changelog:
This patch is separate from:
https://lore.kernel.org/linux-riscv/20220808071318.3335746-1-guoren@kernel.org/
Peter & David have commented on it:
https://lore.kernel.org/linux-riscv/YsK4Z9w0tFtgkni8@hirez.programming.kicks-ass.net/
---
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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next reply other threads:[~2023-07-19 7:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-19 7:00 guoren [this message]
2023-07-23 2:07 ` [PATCH] asm-generic: ticket-lock: Optimize arch_spin_value_unlocked Waiman Long
2023-07-31 2:40 ` Guo Ren
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