From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS Date: Thu, 17 Apr 2014 17:46:27 -0400 Message-ID: <53504BB3.4010009@hp.com> References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-6-git-send-email-Waiman.Long@hp.com> <20140417155649.GR11096@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140417155649.GR11096@twins.programming.kicks-ass.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Zijlstra Cc: linux-arch@vger.kernel.org, Rik van Riel , Raghavendra K T , Gleb Natapov , kvm@vger.kernel.org, Konrad Rzeszutek Wilk , Scott J Norton , x86@kernel.org, Paolo Bonzini , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Chegu Vinod , David Vrabel , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Thomas Gleixner , "Paul E. McKenney" , Linus Torvalds , Oleg Nesterov List-Id: linux-arch.vger.kernel.org On 04/17/2014 11:56 AM, Peter Zijlstra wrote: > On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote: >> +struct __qspinlock { >> + union { >> + atomic_t val; >> + struct { >> +#ifdef __LITTLE_ENDIAN >> + u16 locked_pending; >> + u16 tail; >> +#else >> + u16 tail; >> + u16 locked_pending; >> +#endif >> + }; >> + }; >> +}; >> + >> +/** >> + * clear_pending_set_locked - take ownership and clear the pending bit. >> + * @lock: Pointer to queue spinlock structure >> + * @val : Current value of the queue spinlock 32-bit word >> + * >> + * *,1,0 -> *,0,1 >> + */ >> +static __always_inline void >> +clear_pending_set_locked(struct qspinlock *lock, u32 val) >> +{ >> + struct __qspinlock *l = (void *)lock; >> + >> + ACCESS_ONCE(l->locked_pending) = 1; > You lost the __constant_le16_to_cpu(_Q_LOCKED_VAL) there. The > unconditional 1 is wrong. You also have to flip the bytes in > locked_pending. I don't think that is wrong. The lock byte is in the least significant 8 bits and the pending byte is the next higher significant 8 bits irrespective of the endian-ness. So a value of 1 in a 16-bit context means the lock byte is set, but the pending byte is cleared. The name "locked_pending" doesn't mean that locked variable is in a lower address than pending. -Longman From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g4t3427.houston.hp.com ([15.201.208.55]:10955 "EHLO g4t3427.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001AbaDQVqc (ORCPT ); Thu, 17 Apr 2014 17:46:32 -0400 Message-ID: <53504BB3.4010009@hp.com> Date: Thu, 17 Apr 2014 17:46:27 -0400 From: Waiman Long MIME-Version: 1.0 Subject: Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-6-git-send-email-Waiman.Long@hp.com> <20140417155649.GR11096@twins.programming.kicks-ass.net> In-Reply-To: <20140417155649.GR11096@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Paolo Bonzini , Konrad Rzeszutek Wilk , "Paul E. McKenney" , Rik van Riel , Linus Torvalds , Raghavendra K T , David Vrabel , Oleg Nesterov , Gleb Natapov , Scott J Norton , Chegu Vinod Message-ID: <20140417214627.MmxgQ7yVKe6gK9PFjGGEJFiGi0pG6YnR5xQWc0aUp0I@z> On 04/17/2014 11:56 AM, Peter Zijlstra wrote: > On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote: >> +struct __qspinlock { >> + union { >> + atomic_t val; >> + struct { >> +#ifdef __LITTLE_ENDIAN >> + u16 locked_pending; >> + u16 tail; >> +#else >> + u16 tail; >> + u16 locked_pending; >> +#endif >> + }; >> + }; >> +}; >> + >> +/** >> + * clear_pending_set_locked - take ownership and clear the pending bit. >> + * @lock: Pointer to queue spinlock structure >> + * @val : Current value of the queue spinlock 32-bit word >> + * >> + * *,1,0 -> *,0,1 >> + */ >> +static __always_inline void >> +clear_pending_set_locked(struct qspinlock *lock, u32 val) >> +{ >> + struct __qspinlock *l = (void *)lock; >> + >> + ACCESS_ONCE(l->locked_pending) = 1; > You lost the __constant_le16_to_cpu(_Q_LOCKED_VAL) there. The > unconditional 1 is wrong. You also have to flip the bytes in > locked_pending. I don't think that is wrong. The lock byte is in the least significant 8 bits and the pending byte is the next higher significant 8 bits irrespective of the endian-ness. So a value of 1 in a 16-bit context means the lock byte is set, but the pending byte is cleared. The name "locked_pending" doesn't mean that locked variable is in a lower address than pending. -Longman