From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v10 10/19] qspinlock, x86: Allow unfair spinlock in a virtual guest Date: Mon, 19 May 2014 16:30:22 -0400 Message-ID: <537A69DE.5080000@hp.com> References: <1399474907-22206-1-git-send-email-Waiman.Long@hp.com> <1399474907-22206-11-git-send-email-Waiman.Long@hp.com> <20140508191228.GS2844@laptop.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: <20140508191228.GS2844@laptop.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 , Oleg Nesterov , 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 , Boris Ostrovsky List-Id: linux-arch.vger.kernel.org On 05/08/2014 03:12 PM, Peter Zijlstra wrote: > On Wed, May 07, 2014 at 11:01:38AM -0400, Waiman Long wrote: > > > No, we want the unfair thing for VIRT, not PARAVIRT. > Yes, you are right. I will change that to VIRT. >> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c >> index 9e7659e..10e87e1 100644 >> --- a/kernel/locking/qspinlock.c >> +++ b/kernel/locking/qspinlock.c >> @@ -227,6 +227,14 @@ static __always_inline int get_qlock(struct qspinlock *lock) >> { >> struct __qspinlock *l = (void *)lock; >> >> +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS >> + if (static_key_false(¶virt_unfairlocks_enabled)) >> + /* >> + * Need to use atomic operation to get the lock when >> + * lock stealing can happen. >> + */ >> + return cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0; > That's missing {}. It is a single statement which doesn't need braces according to kernel coding style. I could move the comments up a bit to make it easier to read. >> +#endif > >> barrier(); >> ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL; >> barrier(); > > But no, what you want is: > > static __always_inline bool virt_lock(struct qspinlock *lock) > { > #ifdef CONFIG_VIRT_MUCK > if (static_key_false(&virt_unfairlocks_enabled)) { > while (!queue_spin_trylock(lock)) > cpu_relax(); > > return true; > } > #else > return false; > } > > > void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) > { > if (virt_lock(lock)) > return; > > ... > } This is a possible way of doing it. I can do that in the patch series to simplify it. Hopefully that will speed up the review process and get it done quicker. -Longman From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g4t3425.houston.hp.com ([15.201.208.53]:25946 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752421AbaESUa2 (ORCPT ); Mon, 19 May 2014 16:30:28 -0400 Message-ID: <537A69DE.5080000@hp.com> Date: Mon, 19 May 2014 16:30:22 -0400 From: Waiman Long MIME-Version: 1.0 Subject: Re: [PATCH v10 10/19] qspinlock, x86: Allow unfair spinlock in a virtual guest References: <1399474907-22206-1-git-send-email-Waiman.Long@hp.com> <1399474907-22206-11-git-send-email-Waiman.Long@hp.com> <20140508191228.GS2844@laptop.programming.kicks-ass.net> In-Reply-To: <20140508191228.GS2844@laptop.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 , Boris Ostrovsky , "Paul E. McKenney" , Rik van Riel , Linus Torvalds , Raghavendra K T , David Vrabel , Oleg Nesterov , Gleb Natapov , Scott J Norton , Chegu Vinod Message-ID: <20140519203022.30HVv2PJw_1gVfSxQgmwHc9S3vHfFpUyZnwMF5aWmHk@z> On 05/08/2014 03:12 PM, Peter Zijlstra wrote: > On Wed, May 07, 2014 at 11:01:38AM -0400, Waiman Long wrote: > > > No, we want the unfair thing for VIRT, not PARAVIRT. > Yes, you are right. I will change that to VIRT. >> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c >> index 9e7659e..10e87e1 100644 >> --- a/kernel/locking/qspinlock.c >> +++ b/kernel/locking/qspinlock.c >> @@ -227,6 +227,14 @@ static __always_inline int get_qlock(struct qspinlock *lock) >> { >> struct __qspinlock *l = (void *)lock; >> >> +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS >> + if (static_key_false(¶virt_unfairlocks_enabled)) >> + /* >> + * Need to use atomic operation to get the lock when >> + * lock stealing can happen. >> + */ >> + return cmpxchg(&l->locked, 0, _Q_LOCKED_VAL) == 0; > That's missing {}. It is a single statement which doesn't need braces according to kernel coding style. I could move the comments up a bit to make it easier to read. >> +#endif > >> barrier(); >> ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL; >> barrier(); > > But no, what you want is: > > static __always_inline bool virt_lock(struct qspinlock *lock) > { > #ifdef CONFIG_VIRT_MUCK > if (static_key_false(&virt_unfairlocks_enabled)) { > while (!queue_spin_trylock(lock)) > cpu_relax(); > > return true; > } > #else > return false; > } > > > void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) > { > if (virt_lock(lock)) > return; > > ... > } This is a possible way of doing it. I can do that in the patch series to simplify it. Hopefully that will speed up the review process and get it done quicker. -Longman