linux-kernel - [PATCH 6/6] MIPS: cmpxchg: Use cmpxchg_local() for {cmp_}xchg

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Date:   Wed, 27 Jan 2021 21:36:27 +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 6/6] MIPS: cmpxchg: Use cmpxchg_local() for {cmp_}xchg_small()

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

It makes no sense to fold smp_mb__before_llsc()/smp_llsc_mb() again and
again, leave only one barrier pair in the outer function.

This removes one SYNCW from __xchg_small() and brings around 10%
performance improvement in a tight spinlock loop with 6 threads on a 6 core
Octeon.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
---
 arch/mips/kernel/cmpxchg.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kernel/cmpxchg.c b/arch/mips/kernel/cmpxchg.c
index 89107de..122e85f 100644
--- a/arch/mips/kernel/cmpxchg.c
+++ b/arch/mips/kernel/cmpxchg.c
@@ -41,7 +41,7 @@ unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int s
 	do {
 		old32 = load32;
 		new32 = (load32 & ~mask) | (val << shift);
-		load32 = cmpxchg(ptr32, old32, new32);
+		load32 = cmpxchg_local(ptr32, old32, new32);
 	} while (load32 != old32);
 
 	return (load32 & mask) >> shift;
@@ -97,7 +97,7 @@ unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old,
 		 */
 		old32 = (load32 & ~mask) | (old << shift);
 		new32 = (load32 & ~mask) | (new << shift);
-		load32 = cmpxchg(ptr32, old32, new32);
+		load32 = cmpxchg_local(ptr32, old32, new32);
 		if (load32 == old32)
 			return old;
 	}
-- 
2.10.2