From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: [RFC PATCH-tip/locking/core v3 03/10] locking/rwsem: Make rwsem_spin_on_owner() return a tri-state value Date: Fri, 17 Jun 2016 11:41:29 -0400 Message-ID: <1466178096-5623-4-git-send-email-Waiman.Long@hpe.com> References: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Return-path: In-Reply-To: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Davidlohr Bueso , Jason Low , Dave Chinner , Jonathan Corbet , Scott J Norton , Douglas Hatch , Waiman Long List-Id: linux-arch.vger.kernel.org This patch modifies rwsem_spin_on_owner() to return a tri-state value to better reflect the state of lock holder which enables us to make a better decision of what to do next. Signed-off-by: Waiman Long --- kernel/locking/rwsem-xadd.c | 14 +++++++++----- 1 files changed, 9 insertions(+), 5 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 29027c6..198b732 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -360,9 +360,13 @@ done: } /* - * Return true only if we can still spin on the owner field of the rwsem. + * Return the folowing three values depending on the lock owner state. + * 1 when owner has changed and no reader is detected yet. + * 0 when owner has change and/or owner is a reader. + * -1 when optimistic spinning has to stop because either the owner stops + * running or its timeslice has been used up. */ -static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) +static noinline int rwsem_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner = READ_ONCE(sem->owner); @@ -382,7 +386,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) /* abort spinning when need_resched or owner is not running */ if (!owner->on_cpu || need_resched()) { rcu_read_unlock(); - return false; + return -1; } cpu_relax_lowlatency(); @@ -393,7 +397,7 @@ out: * If there is a new owner or the owner is not set, we continue * spinning. */ - return !rwsem_owner_is_reader(READ_ONCE(sem->owner)); + return rwsem_owner_is_reader(READ_ONCE(sem->owner)) ? 0 : 1; } static bool rwsem_optimistic_spin(struct rw_semaphore *sem) @@ -416,7 +420,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) * 2) readers own the lock as we can't determine if they are * actively running or not. */ - while (rwsem_spin_on_owner(sem)) { + while (rwsem_spin_on_owner(sem) > 0) { /* * Try to acquire the lock */ -- 1.7.1 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g4t3426.houston.hpe.com ([15.241.140.75]:39184 "EHLO g4t3426.houston.hpe.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933743AbcFQPmQ (ORCPT ); Fri, 17 Jun 2016 11:42:16 -0400 From: Waiman Long Subject: [RFC PATCH-tip/locking/core v3 03/10] locking/rwsem: Make rwsem_spin_on_owner() return a tri-state value Date: Fri, 17 Jun 2016 11:41:29 -0400 Message-ID: <1466178096-5623-4-git-send-email-Waiman.Long@hpe.com> In-Reply-To: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> References: <1466178096-5623-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, Davidlohr Bueso , Jason Low , Dave Chinner , Jonathan Corbet , Scott J Norton , Douglas Hatch , Waiman Long Message-ID: <20160617154129.BGH6are7G2z70NcxUCOaGbx075a-yKxs_-bcn5X0f-4@z> This patch modifies rwsem_spin_on_owner() to return a tri-state value to better reflect the state of lock holder which enables us to make a better decision of what to do next. Signed-off-by: Waiman Long --- kernel/locking/rwsem-xadd.c | 14 +++++++++----- 1 files changed, 9 insertions(+), 5 deletions(-) diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index 29027c6..198b732 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -360,9 +360,13 @@ done: } /* - * Return true only if we can still spin on the owner field of the rwsem. + * Return the folowing three values depending on the lock owner state. + * 1 when owner has changed and no reader is detected yet. + * 0 when owner has change and/or owner is a reader. + * -1 when optimistic spinning has to stop because either the owner stops + * running or its timeslice has been used up. */ -static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) +static noinline int rwsem_spin_on_owner(struct rw_semaphore *sem) { struct task_struct *owner = READ_ONCE(sem->owner); @@ -382,7 +386,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) /* abort spinning when need_resched or owner is not running */ if (!owner->on_cpu || need_resched()) { rcu_read_unlock(); - return false; + return -1; } cpu_relax_lowlatency(); @@ -393,7 +397,7 @@ out: * If there is a new owner or the owner is not set, we continue * spinning. */ - return !rwsem_owner_is_reader(READ_ONCE(sem->owner)); + return rwsem_owner_is_reader(READ_ONCE(sem->owner)) ? 0 : 1; } static bool rwsem_optimistic_spin(struct rw_semaphore *sem) @@ -416,7 +420,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem) * 2) readers own the lock as we can't determine if they are * actively running or not. */ - while (rwsem_spin_on_owner(sem)) { + while (rwsem_spin_on_owner(sem) > 0) { /* * Try to acquire the lock */ -- 1.7.1