linux-kernel - [RFC][PATCH 3/5] mips/atomic: Optimize loongson3_llsc

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Date:   Wed, 24 Apr 2019 14:36:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     stern@...land.harvard.edu, akiyks@...il.com,
        andrea.parri@...rulasolutions.com, boqun.feng@...il.com,
        dlustig@...dia.com, dhowells@...hat.com, j.alglave@....ac.uk,
        luc.maranget@...ia.fr, npiggin@...il.com, paulmck@...ux.ibm.com,
        peterz@...radead.org, will.deacon@....com
Cc:     linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        Huacai Chen <chenhc@...ote.com>,
        Huang Pei <huangpei@...ngson.cn>,
        Paul Burton <paul.burton@...s.com>
Subject: [RFC][PATCH 3/5] mips/atomic: Optimize loongson3_llsc_mb()

Now that every single LL/SC loop has loongson_llsc_mb() in front, we
can NO-OP smp_mb__before_llsc() in that case.

While there, remove the superfluous __smp_mb__before_llsc().

Cc: Huacai Chen <chenhc@...ote.com>
Cc: Huang Pei <huangpei@...ngson.cn>
Cc: Paul Burton <paul.burton@...s.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/mips/include/asm/barrier.h |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -221,15 +221,12 @@
 
 #ifdef CONFIG_CPU_CAVIUM_OCTEON
 #define smp_mb__before_llsc() smp_wmb()
-#define __smp_mb__before_llsc() __smp_wmb()
 /* Cause previous writes to become visible on all CPUs as soon as possible */
 #define nudge_writes() __asm__ __volatile__(".set push\n\t"		\
 					    ".set arch=octeon\n\t"	\
 					    "syncw\n\t"			\
 					    ".set pop" : : : "memory")
 #else
-#define smp_mb__before_llsc() smp_llsc_mb()
-#define __smp_mb__before_llsc() smp_llsc_mb()
 #define nudge_writes() mb()
 #endif
 
@@ -264,11 +261,19 @@
  *    This case affects all current Loongson 3 CPUs.
  */
 #ifdef CONFIG_CPU_LOONGSON3_WORKAROUNDS /* Loongson-3's LLSC workaround */
+#define smp_mb__before_llsc()	do { } while (0)
 #define loongson_llsc_mb()	__asm__ __volatile__("sync" : : :"memory")
 #else
 #define loongson_llsc_mb()	do { } while (0)
 #endif
 
+#ifndef smp_mb__before_llsc
+#define smp_mb__before_llsc() smp_llsc_mb()
+#endif
+
+#define __smp_mb__before_atomic()	smp_mb__before_llsc()
+#define __smp_mb__after_atomic()	smp_llsc_mb()
+
 static inline void sync_ginv(void)
 {
 	asm volatile("sync\t%0" :: "i"(STYPE_GINV));