From: Tim Chen <tim.c.chen@linux.intel.com> To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>, Tim Chen <tim.c.chen@linux.intel.com>, Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org> Subject: [PATCH v8 7/9] MCS Lock: Barrier corrections Date: Wed, 02 Oct 2013 15:38:38 -0700 [thread overview] Message-ID: <1380753518.11046.89.camel@schen9-DESK> (raw) In-Reply-To: <cover.1380748401.git.tim.c.chen@linux.intel.com> This patch corrects the way memory barriers are used in the MCS lock and removes ones that are not needed. Also add comments on all barriers. Signed-off-by: Jason Low <jason.low2@hp.com> --- include/linux/mcs_spinlock.h | 13 +++++++++++-- 1 files changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h index 96f14299..93d445d 100644 --- a/include/linux/mcs_spinlock.h +++ b/include/linux/mcs_spinlock.h @@ -36,16 +36,19 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) node->locked = 0; node->next = NULL; + /* xchg() provides a memory barrier */ prev = xchg(lock, node); if (likely(prev == NULL)) { /* Lock acquired */ return; } ACCESS_ONCE(prev->next) = node; - smp_wmb(); /* Wait until the lock holder passes the lock down */ while (!ACCESS_ONCE(node->locked)) arch_mutex_cpu_relax(); + + /* Make sure subsequent operations happen after the lock is acquired */ + smp_rmb(); } /* @@ -58,6 +61,7 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod if (likely(!next)) { /* + * cmpxchg() provides a memory barrier. * Release the lock by setting it to NULL */ if (likely(cmpxchg(lock, node, NULL) == node)) @@ -65,9 +69,14 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod /* Wait until the next pointer is set */ while (!(next = ACCESS_ONCE(node->next))) arch_mutex_cpu_relax(); + } else { + /* + * Make sure all operations within the critical section + * happen before the lock is released. + */ + smp_wmb(); } ACCESS_ONCE(next->locked) = 1; - smp_wmb(); } #endif /* __LINUX_MCS_SPINLOCK_H */ -- 1.7.4.4
WARNING: multiple messages have this Message-ID (diff)
From: Tim Chen <tim.c.chen@linux.intel.com> To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, "Paul E.McKenney" <paulmck@linux.vnet.ibm.com>, Tim Chen <tim.c.chen@linux.intel.com>, Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org> Subject: [PATCH v8 7/9] MCS Lock: Barrier corrections Date: Wed, 02 Oct 2013 15:38:38 -0700 [thread overview] Message-ID: <1380753518.11046.89.camel@schen9-DESK> (raw) In-Reply-To: <cover.1380748401.git.tim.c.chen@linux.intel.com> This patch corrects the way memory barriers are used in the MCS lock and removes ones that are not needed. Also add comments on all barriers. Signed-off-by: Jason Low <jason.low2@hp.com> --- include/linux/mcs_spinlock.h | 13 +++++++++++-- 1 files changed, 11 insertions(+), 2 deletions(-) diff --git a/include/linux/mcs_spinlock.h b/include/linux/mcs_spinlock.h index 96f14299..93d445d 100644 --- a/include/linux/mcs_spinlock.h +++ b/include/linux/mcs_spinlock.h @@ -36,16 +36,19 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) node->locked = 0; node->next = NULL; + /* xchg() provides a memory barrier */ prev = xchg(lock, node); if (likely(prev == NULL)) { /* Lock acquired */ return; } ACCESS_ONCE(prev->next) = node; - smp_wmb(); /* Wait until the lock holder passes the lock down */ while (!ACCESS_ONCE(node->locked)) arch_mutex_cpu_relax(); + + /* Make sure subsequent operations happen after the lock is acquired */ + smp_rmb(); } /* @@ -58,6 +61,7 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod if (likely(!next)) { /* + * cmpxchg() provides a memory barrier. * Release the lock by setting it to NULL */ if (likely(cmpxchg(lock, node, NULL) == node)) @@ -65,9 +69,14 @@ static void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *nod /* Wait until the next pointer is set */ while (!(next = ACCESS_ONCE(node->next))) arch_mutex_cpu_relax(); + } else { + /* + * Make sure all operations within the critical section + * happen before the lock is released. + */ + smp_wmb(); } ACCESS_ONCE(next->locked) = 1; - smp_wmb(); } #endif /* __LINUX_MCS_SPINLOCK_H */ -- 1.7.4.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2013-10-02 22:38 UTC|newest] Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <cover.1380748401.git.tim.c.chen@linux.intel.com> 2013-10-02 22:38 ` [PATCH v8 0/9] rwsem performance optimizations Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-03 7:32 ` Ingo Molnar 2013-10-03 7:32 ` Ingo Molnar 2013-10-07 22:57 ` Tim Chen 2013-10-07 22:57 ` Tim Chen 2013-10-09 6:15 ` Ingo Molnar 2013-10-09 6:15 ` Ingo Molnar 2013-10-09 7:28 ` Peter Zijlstra 2013-10-09 7:28 ` Peter Zijlstra 2013-10-10 3:14 ` Linus Torvalds 2013-10-10 3:14 ` Linus Torvalds 2013-10-10 5:03 ` Davidlohr Bueso 2013-10-10 5:03 ` Davidlohr Bueso 2013-10-09 16:34 ` Tim Chen 2013-10-09 16:34 ` Tim Chen 2013-10-10 7:54 ` Ingo Molnar 2013-10-10 7:54 ` Ingo Molnar 2013-10-16 0:09 ` Tim Chen 2013-10-16 0:09 ` Tim Chen 2013-10-16 6:55 ` Ingo Molnar 2013-10-16 6:55 ` Ingo Molnar 2013-10-16 18:28 ` Tim Chen 2013-10-16 18:28 ` Tim Chen 2013-11-04 22:36 ` Tim Chen 2013-11-04 22:36 ` Tim Chen 2013-10-16 21:55 ` Tim Chen 2013-10-16 21:55 ` Tim Chen 2013-10-18 6:52 ` Ingo Molnar 2013-10-18 6:52 ` Ingo Molnar 2013-10-02 22:38 ` [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 2/9] rwsem: remove 'out' label in do_wake Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 3/9] rwsem: remove try_reader_grant label do_wake Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 4/9] rwsem/wake: check lock before do atomic update Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 5/9] MCS Lock: Restructure the MCS lock defines and locking code into its own file Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-08 19:51 ` Rafael Aquini 2013-10-08 19:51 ` Rafael Aquini 2013-10-08 20:34 ` Tim Chen 2013-10-08 20:34 ` Tim Chen 2013-10-08 21:31 ` Rafael Aquini 2013-10-08 21:31 ` Rafael Aquini 2013-10-02 22:38 ` [PATCH v8 6/9] MCS Lock: optimizations and extra comments Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` Tim Chen [this message] 2013-10-02 22:38 ` [PATCH v8 7/9] MCS Lock: Barrier corrections Tim Chen 2013-10-02 22:38 ` [PATCH v8 8/9] rwsem: do optimistic spinning for writer lock acquisition Tim Chen 2013-10-02 22:38 ` Tim Chen 2013-10-02 22:38 ` [PATCH v8 9/9] rwsem: reduce spinlock contention in wakeup code path Tim Chen 2013-10-02 22:38 ` Tim Chen
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