From a91f2a1dba44c29cd0d75edd8787f4469092ae8f Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Tue, 1 Oct 2019 21:53:38 +0000 Subject: MIPS: cmpxchg: Omit redundant barriers for Loongson3 When building a kernel configured to support Loongson3 LL/SC workarounds (ie. CONFIG_CPU_LOONGSON3_WORKAROUNDS=y) the inline assembly in __xchg_asm() & __cmpxchg_asm() already emits completion barriers, and as such we don't need to emit extra barriers from the xchg() or cmpxchg() macros. Add compile-time constant checks causing us to omit the redundant memory barriers. Signed-off-by: Paul Burton Cc: linux-mips@vger.kernel.org Cc: Huacai Chen Cc: Jiaxun Yang Cc: linux-kernel@vger.kernel.org --- arch/mips/include/asm/cmpxchg.h | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/arch/mips/include/asm/cmpxchg.h b/arch/mips/include/asm/cmpxchg.h index fc121d20a980..820df68e32e1 100644 --- a/arch/mips/include/asm/cmpxchg.h +++ b/arch/mips/include/asm/cmpxchg.h @@ -94,7 +94,13 @@ static inline unsigned long __xchg(volatile void *ptr, unsigned long x, ({ \ __typeof__(*(ptr)) __res; \ \ - smp_mb__before_llsc(); \ + /* \ + * In the Loongson3 workaround case __xchg_asm() already \ + * contains a completion barrier prior to the LL, so we don't \ + * need to emit an extra one here. \ + */ \ + if (!__SYNC_loongson3_war) \ + smp_mb__before_llsc(); \ \ __res = (__typeof__(*(ptr))) \ __xchg((ptr), (unsigned long)(x), sizeof(*(ptr))); \ @@ -179,9 +185,23 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old, ({ \ __typeof__(*(ptr)) __res; \ \ - smp_mb__before_llsc(); \ + /* \ + * In the Loongson3 workaround case __cmpxchg_asm() already \ + * contains a completion barrier prior to the LL, so we don't \ + * need to emit an extra one here. \ + */ \ + if (!__SYNC_loongson3_war) \ + smp_mb__before_llsc(); \ + \ __res = cmpxchg_local((ptr), (old), (new)); \ - smp_llsc_mb(); \ + \ + /* \ + * In the Loongson3 workaround case __cmpxchg_asm() already \ + * contains a completion barrier after the SC, so we don't \ + * need to emit an extra one here. \ + */ \ + if (!__SYNC_loongson3_war) \ + smp_llsc_mb(); \ \ __res; \ }) -- cgit