From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751532AbeBVVqK (ORCPT ); Thu, 22 Feb 2018 16:46:10 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:39532 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbeBVVqH (ORCPT ); Thu, 22 Feb 2018 16:46:07 -0500 Date: Thu, 22 Feb 2018 13:46:25 -0800 From: "Paul E. McKenney" To: Andrea Parri Cc: Ingo Molnar , Peter Zijlstra , Alan Stern , Ivan Kokshaysky , Matt Turner , Richard Henderson , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] locking/xchg/alpha: Use smp_mb() in place of __ASM__MB Reply-To: paulmck@linux.vnet.ibm.com References: <1519291469-5702-1-git-send-email-parri.andrea@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1519291469-5702-1-git-send-email-parri.andrea@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18022221-0040-0000-0000-000003FBA110 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008578; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000254; SDB=6.00993612; UDB=6.00504897; IPR=6.00772952; MB=3.00019694; MTD=3.00000008; XFM=3.00000015; UTC=2018-02-22 21:46:04 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18022221-0041-0000-0000-000007FCA824 Message-Id: <20180222214625.GM2855@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-02-22_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=18 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1802220269 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Signed-off-by: Andrea Parri 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 > Cc: Peter Zijlstra > Cc: Paul E. McKenney > Cc: Alan Stern > Cc: Ivan Kokshaysky > Cc: Matt Turner > Cc: Richard Henderson > Cc: linux-alpha@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 > @@ -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 >