From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753532AbaA3Po3 (ORCPT ); Thu, 30 Jan 2014 10:44:29 -0500 Received: from merlin.infradead.org ([205.233.59.134]:53460 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753137AbaA3Po1 (ORCPT ); Thu, 30 Jan 2014 10:44:27 -0500 Date: Thu, 30 Jan 2014 16:44:00 +0100 From: Peter Zijlstra To: Waiman Long Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Andrew Morton , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , Linus Torvalds , Raghavendra K T , George Spelvin , Tim Chen , "Aswin Chandramouleeswaran\"" , Scott J Norton , will@willdeacon.co.uk Subject: Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation Message-ID: <20140130154400.GB5126@laptop.programming.kicks-ass.net> References: <1390537731-45996-1-git-send-email-Waiman.Long@hp.com> <20140130130453.GB2936@laptop.programming.kicks-ass.net> <20140130151715.GA5126@laptop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140130151715.GA5126@laptop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 30, 2014 at 04:17:15PM +0100, Peter Zijlstra wrote: > --- /dev/null > +++ b/arch/x86/include/asm/qrwlock.h > @@ -0,0 +1,18 @@ > +#ifndef _ASM_X86_QRWLOCK_H > +#define _ASM_X86_QRWLOCK_H > + > +#include > + > +#if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE) > +#define queue_write_unlock queue_write_unlock > +static inline void queue_write_unlock(struct qrwlock *lock) > +{ > + barrier(); > + ACCESS_ONCE(*(u8 *)&lock->cnts) = 0; > +} > +#endif > + > +#include > + > +#endif /* _ASM_X86_QRWLOCK_H */ > + > +/** > + * queue_read_unlock - release read lock of a queue rwlock > + * @lock : Pointer to queue rwlock structure > + */ > +static inline void queue_read_unlock(struct qrwlock *lock) > +{ > + /* > + * Atomically decrement the reader count > + */ > + smp_mb__before_atomic_dec(); > + atomic_sub(_QR_BIAS, &lock->cnts); > +} > + > +#ifndef queue_write_unlock > +/** > + * queue_write_unlock - release write lock of a queue rwlock > + * @lock : Pointer to queue rwlock structure > + */ > +static inline void queue_write_unlock(struct qrwlock *lock) > +{ > + /* > + * If the writer field is atomic, it can be cleared directly. > + * Otherwise, an atomic subtraction will be used to clear it. > + */ > + smp_mb__before_atomic_dec(); > + atomic_sub(_QW_LOCKED, &lock->cnts); > +} > +#endif Something like this would work for ARM and PPC, although I didn't do the PPC variant of atomic_sub_release(). --- a/arch/arm64/include/asm/atomic.h +++ b/arch/arm64/include/asm/atomic.h @@ -90,6 +90,21 @@ static inline void atomic_sub(int i, ato : "cc"); } +static inline void atomic_sub_release(int i, atomic_t *v) +{ + unsigned long tmp; + int result; + + asm volatile("// atomic_sub\n" +"1: ldxr %w0, %2\n" +" sub %w0, %w0, %w3\n" +" stlxr %w1, %w0, %2\n" +" cbnz %w1, 1b" + : "=&r" (result), "=&r" (tmp), "+Q" (v->counter) + : "Ir" (i) + : "cc"); +} + static inline int atomic_sub_return(int i, atomic_t *v) { unsigned long tmp; --- /dev/null +++ b/arch/arm64/include/asm/qrwlock.h @@ -0,0 +1,21 @@ +#ifndef _ASM_ARM64_QRWLOCK_H +#define _ASM_ARM64_QRWLOCK_H + +#include + +#define queue_read_unlock queue_read_unlock +static inline void queue_read_unlock(struct qrwlock *lock) +{ + atomic_sub_release(_QR_BIAS, &lock->cnts); +} + +#define queue_write_unlock queue_write_unlock +static inline void queue_write_unlock(struct qrwlock *lock) +{ + atomic_sub_release(_QW_LOCKED, &lock->cnts); +} + +#include + +#endif /* _ASM_ARM64_QRWLOCK_H */ + --- a/include/asm-generic/qrwlock.h +++ b/include/asm-generic/qrwlock.h @@ -122,6 +122,7 @@ static inline void queue_write_lock(stru queue_write_lock_slowpath(lock); } +#ifndef queue_read_unlock /** * queue_read_unlock - release read lock of a queue rwlock * @lock : Pointer to queue rwlock structure @@ -134,6 +135,7 @@ static inline void queue_read_unlock(str smp_mb__before_atomic_dec(); atomic_sub(_QR_BIAS, &lock->cnts); } +#endif #ifndef queue_write_unlock /**