On Thu, Feb 22, 2018 at 10:24:29AM +0100, Andrea Parri wrote: > Replace each occurrence of __ASM__MB with a (trailing) smp_mb() in > xchg(), cmpxchg(), and remove the now unused __ASM__MB definitions; > this improves readability, with no additional synchronization cost. > > Suggested-by: Will Deacon <will.dea...@arm.com> > Signed-off-by: Andrea Parri <parri.and...@gmail.com>
I am a bit confused by the use of out-of-line branches to do a backwards branch, but those were in place to start with. Maybe the point is to defeat backwards-branch prediction or some such. Regardless... Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Cc: Alan Stern <st...@rowland.harvard.edu> > Cc: Ivan Kokshaysky <i...@jurassic.park.msu.ru> > Cc: Matt Turner <matts...@gmail.com> > Cc: Richard Henderson <r...@twiddle.net> > Cc: linux-al...@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- > arch/alpha/include/asm/cmpxchg.h | 6 ------ > arch/alpha/include/asm/xchg.h | 16 ++++++++-------- > 2 files changed, 8 insertions(+), 14 deletions(-) > > diff --git a/arch/alpha/include/asm/cmpxchg.h > b/arch/alpha/include/asm/cmpxchg.h > index 46ebf14aed4e5..8a2b331e43feb 100644 > --- a/arch/alpha/include/asm/cmpxchg.h > +++ b/arch/alpha/include/asm/cmpxchg.h > @@ -6,7 +6,6 @@ > * Atomic exchange routines. > */ > > -#define __ASM__MB > #define ____xchg(type, args...) __xchg ## type ## _local(args) > #define ____cmpxchg(type, args...) __cmpxchg ## type ## _local(args) > #include <asm/xchg.h> > @@ -33,10 +32,6 @@ > cmpxchg_local((ptr), (o), (n)); \ > }) > > -#ifdef CONFIG_SMP > -#undef __ASM__MB > -#define __ASM__MB "\tmb\n" > -#endif > #undef ____xchg > #undef ____cmpxchg > #define ____xchg(type, args...) __xchg ##type(args) > @@ -64,7 +59,6 @@ > cmpxchg((ptr), (o), (n)); \ > }) > > -#undef __ASM__MB > #undef ____cmpxchg > > #endif /* _ALPHA_CMPXCHG_H */ > diff --git a/arch/alpha/include/asm/xchg.h b/arch/alpha/include/asm/xchg.h > index e2660866ce972..e1facf6fc2446 100644 > --- a/arch/alpha/include/asm/xchg.h > +++ b/arch/alpha/include/asm/xchg.h > @@ -28,12 +28,12 @@ ____xchg(_u8, volatile char *m, unsigned long val) > " or %1,%2,%2\n" > " stq_c %2,0(%3)\n" > " beq %2,2f\n" > - __ASM__MB > ".subsection 2\n" > "2: br 1b\n" > ".previous" > : "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64) > : "r" ((long)m), "1" (val) : "memory"); > + smp_mb(); > > return ret; > } > @@ -52,12 +52,12 @@ ____xchg(_u16, volatile short *m, unsigned long val) > " or %1,%2,%2\n" > " stq_c %2,0(%3)\n" > " beq %2,2f\n" > - __ASM__MB > ".subsection 2\n" > "2: br 1b\n" > ".previous" > : "=&r" (ret), "=&r" (val), "=&r" (tmp), "=&r" (addr64) > : "r" ((long)m), "1" (val) : "memory"); > + smp_mb(); > > return ret; > } > @@ -72,12 +72,12 @@ ____xchg(_u32, volatile int *m, unsigned long val) > " bis $31,%3,%1\n" > " stl_c %1,%2\n" > " beq %1,2f\n" > - __ASM__MB > ".subsection 2\n" > "2: br 1b\n" > ".previous" > : "=&r" (val), "=&r" (dummy), "=m" (*m) > : "rI" (val), "m" (*m) : "memory"); > + smp_mb(); > > return val; > } > @@ -92,12 +92,12 @@ ____xchg(_u64, volatile long *m, unsigned long val) > " bis $31,%3,%1\n" > " stq_c %1,%2\n" > " beq %1,2f\n" > - __ASM__MB > ".subsection 2\n" > "2: br 1b\n" > ".previous" > : "=&r" (val), "=&r" (dummy), "=m" (*m) > : "rI" (val), "m" (*m) : "memory"); > + smp_mb(); > > return val; > } > @@ -150,12 +150,12 @@ ____cmpxchg(_u8, volatile char *m, unsigned char old, > unsigned char new) > " stq_c %2,0(%4)\n" > " beq %2,3f\n" > "2:\n" > - __ASM__MB > ".subsection 2\n" > "3: br 1b\n" > ".previous" > : "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64) > : "r" ((long)m), "Ir" (old), "1" (new) : "memory"); > + smp_mb(); > > return prev; > } > @@ -177,12 +177,12 @@ ____cmpxchg(_u16, volatile short *m, unsigned short > old, unsigned short new) > " stq_c %2,0(%4)\n" > " beq %2,3f\n" > "2:\n" > - __ASM__MB > ".subsection 2\n" > "3: br 1b\n" > ".previous" > : "=&r" (prev), "=&r" (new), "=&r" (tmp), "=&r" (cmp), "=&r" (addr64) > : "r" ((long)m), "Ir" (old), "1" (new) : "memory"); > + smp_mb(); > > return prev; > } > @@ -200,12 +200,12 @@ ____cmpxchg(_u32, volatile int *m, int old, int new) > " stl_c %1,%2\n" > " beq %1,3f\n" > "2:\n" > - __ASM__MB > ".subsection 2\n" > "3: br 1b\n" > ".previous" > : "=&r"(prev), "=&r"(cmp), "=m"(*m) > : "r"((long) old), "r"(new), "m"(*m) : "memory"); > + smp_mb(); > > return prev; > } > @@ -223,12 +223,12 @@ ____cmpxchg(_u64, volatile long *m, unsigned long old, > unsigned long new) > " stq_c %1,%2\n" > " beq %1,3f\n" > "2:\n" > - __ASM__MB > ".subsection 2\n" > "3: br 1b\n" > ".previous" > : "=&r"(prev), "=&r"(cmp), "=m"(*m) > : "r"((long) old), "r"(new), "m"(*m) : "memory"); > + smp_mb(); > > return prev; > } > -- > 2.7.4 >
