linux-kernel - [PATCH 2/6] MIPS: Implement atomic_cmpxchg

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Message-Id: <20210127203627.47510-3-alexander.sverdlin@nokia.com>
Date:   Wed, 27 Jan 2021 21:36:23 +0100
From:   Alexander A Sverdlin <alexander.sverdlin@...ia.com>
To:     Paul Burton <paul.burton@...tec.com>, linux-mips@...r.kernel.org
Cc:     Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] MIPS: Implement atomic_cmpxchg_relaxed()

From: Alexander Sverdlin <alexander.sverdlin@...ia.com>

This will save one SYNCW on Octeon and improve tight
uncontended spinlock loop performance by 17%.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
---
 arch/mips/include/asm/atomic.h  | 3 +++
 arch/mips/include/asm/cmpxchg.h | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/arch/mips/include/asm/atomic.h b/arch/mips/include/asm/atomic.h
index f904084..a4e5116 100644
--- a/arch/mips/include/asm/atomic.h
+++ b/arch/mips/include/asm/atomic.h
@@ -264,4 +264,7 @@ ATOMIC_SIP_OP(atomic64, s64, dsubu, lld, scd)
 
 #undef ATOMIC_SIP_OP
 
+#define atomic_cmpxchg_relaxed(v, o, n) \
+	(cmpxchg_relaxed(&((v)->counter), (o), (n)))
+
 #endif /* _ASM_ATOMIC_H */
diff --git a/arch/mips/include/asm/cmpxchg.h b/arch/mips/include/asm/cmpxchg.h
index 5b0b3a6..620f01a 100644
--- a/arch/mips/include/asm/cmpxchg.h
+++ b/arch/mips/include/asm/cmpxchg.h
@@ -182,6 +182,8 @@ unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
 			  (unsigned long)(__typeof__(*(ptr)))(new),	\
 			  sizeof(*(ptr))))
 
+#define cmpxchg_relaxed		cmpxchg_local
+
 #define cmpxchg(ptr, old, new)						\
 ({									\
 	__typeof__(*(ptr)) __res;					\
-- 
2.10.2