From: Will Deacon <will.deacon@arm.com> To: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, peterz@infradead.org, mingo@kernel.org, boqun.feng@gmail.com, paulmck@linux.vnet.ibm.com, catalin.marinas@arm.com, Jason Low <jason.low2@hp.com>, Will Deacon <will.deacon@arm.com> Subject: [PATCH 05/10] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Date: Thu, 5 Apr 2018 17:59:02 +0100 [thread overview] Message-ID: <1522947547-24081-6-git-send-email-will.deacon@arm.com> (raw) In-Reply-To: <1522947547-24081-1-git-send-email-will.deacon@arm.com> From: Jason Low <jason.low2@hp.com> For qspinlocks on ARM64, we would like to use WFE instead of purely spinning. Qspinlocks internally have lock contenders spin on an MCS lock. Update arch_mcs_spin_lock_contended() such that it uses the new smp_cond_load_acquire() so that ARM64 can also override this spin loop with its own implementation using WFE. On x86, this can also be cheaper than spinning on smp_load_acquire(). Signed-off-by: Jason Low <jason.low2@hp.com> Signed-off-by: Will Deacon <will.deacon@arm.com> --- kernel/locking/mcs_spinlock.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index f046b7ce9dd6..5e10153b4d3c 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -23,13 +23,15 @@ struct mcs_spinlock { #ifndef arch_mcs_spin_lock_contended /* - * Using smp_load_acquire() provides a memory barrier that ensures - * subsequent operations happen after the lock is acquired. + * Using smp_cond_load_acquire() provides the acquire semantics + * required so that subsequent operations happen after the + * lock is acquired. Additionally, some architectures such as + * ARM64 would like to do spin-waiting instead of purely + * spinning, and smp_cond_load_acquire() provides that behavior. */ #define arch_mcs_spin_lock_contended(l) \ do { \ - while (!(smp_load_acquire(l))) \ - cpu_relax(); \ + smp_cond_load_acquire(l, VAL); \ } while (0) #endif -- 2.1.4
WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 05/10] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Date: Thu, 5 Apr 2018 17:59:02 +0100 [thread overview] Message-ID: <1522947547-24081-6-git-send-email-will.deacon@arm.com> (raw) In-Reply-To: <1522947547-24081-1-git-send-email-will.deacon@arm.com> From: Jason Low <jason.low2@hp.com> For qspinlocks on ARM64, we would like to use WFE instead of purely spinning. Qspinlocks internally have lock contenders spin on an MCS lock. Update arch_mcs_spin_lock_contended() such that it uses the new smp_cond_load_acquire() so that ARM64 can also override this spin loop with its own implementation using WFE. On x86, this can also be cheaper than spinning on smp_load_acquire(). Signed-off-by: Jason Low <jason.low2@hp.com> Signed-off-by: Will Deacon <will.deacon@arm.com> --- kernel/locking/mcs_spinlock.h | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h index f046b7ce9dd6..5e10153b4d3c 100644 --- a/kernel/locking/mcs_spinlock.h +++ b/kernel/locking/mcs_spinlock.h @@ -23,13 +23,15 @@ struct mcs_spinlock { #ifndef arch_mcs_spin_lock_contended /* - * Using smp_load_acquire() provides a memory barrier that ensures - * subsequent operations happen after the lock is acquired. + * Using smp_cond_load_acquire() provides the acquire semantics + * required so that subsequent operations happen after the + * lock is acquired. Additionally, some architectures such as + * ARM64 would like to do spin-waiting instead of purely + * spinning, and smp_cond_load_acquire() provides that behavior. */ #define arch_mcs_spin_lock_contended(l) \ do { \ - while (!(smp_load_acquire(l))) \ - cpu_relax(); \ + smp_cond_load_acquire(l, VAL); \ } while (0) #endif -- 2.1.4
next prev parent reply other threads:[~2018-04-05 17:00 UTC|newest] Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-04-05 16:58 [PATCH 00/10] kernel/locking: qspinlock improvements Will Deacon 2018-04-05 16:58 ` Will Deacon 2018-04-05 16:58 ` [PATCH 01/10] locking/qspinlock: Don't spin on pending->locked transition in slowpath Will Deacon 2018-04-05 16:58 ` Will Deacon 2018-04-05 16:58 ` [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon 2018-04-05 16:58 ` Will Deacon 2018-04-05 17:07 ` Peter Zijlstra 2018-04-05 17:07 ` Peter Zijlstra 2018-04-06 15:08 ` Will Deacon 2018-04-06 15:08 ` Will Deacon 2018-04-05 17:13 ` Peter Zijlstra 2018-04-05 17:13 ` Peter Zijlstra 2018-04-05 21:16 ` Waiman Long 2018-04-05 21:16 ` Waiman Long 2018-04-06 15:08 ` Will Deacon 2018-04-06 15:08 ` Will Deacon 2018-04-06 20:50 ` Waiman Long 2018-04-06 20:50 ` Waiman Long 2018-04-06 21:09 ` Paul E. McKenney 2018-04-06 21:09 ` Paul E. McKenney 2018-04-07 8:47 ` Peter Zijlstra 2018-04-07 8:47 ` Peter Zijlstra 2018-04-07 23:37 ` Paul E. McKenney 2018-04-07 23:37 ` Paul E. McKenney 2018-04-09 10:58 ` Will Deacon 2018-04-09 10:58 ` Will Deacon 2018-04-07 9:07 ` Peter Zijlstra 2018-04-07 9:07 ` Peter Zijlstra 2018-04-09 10:58 ` Will Deacon 2018-04-09 10:58 ` Will Deacon 2018-04-09 14:54 ` Will Deacon 2018-04-09 14:54 ` Will Deacon 2018-04-09 15:54 ` Peter Zijlstra 2018-04-09 15:54 ` Peter Zijlstra 2018-04-09 17:19 ` Will Deacon 2018-04-09 17:19 ` Will Deacon 2018-04-10 9:35 ` Peter Zijlstra 2018-04-10 9:35 ` Peter Zijlstra 2018-09-20 16:08 ` Peter Zijlstra 2018-09-20 16:08 ` Peter Zijlstra 2018-09-20 16:22 ` Peter Zijlstra 2018-09-20 16:22 ` Peter Zijlstra 2018-04-09 19:33 ` Waiman Long 2018-04-09 19:33 ` Waiman Long 2018-04-09 17:55 ` Waiman Long 2018-04-09 17:55 ` Waiman Long 2018-04-10 13:49 ` Sasha Levin 2018-04-10 13:49 ` Sasha Levin 2018-04-05 16:59 ` [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 17:19 ` Peter Zijlstra 2018-04-05 17:19 ` Peter Zijlstra 2018-04-06 10:54 ` Will Deacon 2018-04-06 10:54 ` Will Deacon 2018-04-05 16:59 ` [PATCH 04/10] locking/qspinlock: Use atomic_cond_read_acquire Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 16:59 ` Will Deacon [this message] 2018-04-05 16:59 ` [PATCH 05/10] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Will Deacon 2018-04-05 16:59 ` [PATCH 06/10] barriers: Introduce smp_cond_load_relaxed and atomic_cond_read_relaxed Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 17:22 ` Peter Zijlstra 2018-04-05 17:22 ` Peter Zijlstra 2018-04-06 10:55 ` Will Deacon 2018-04-06 10:55 ` Will Deacon 2018-04-05 16:59 ` [PATCH 07/10] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 16:59 ` [PATCH 08/10] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-07 5:23 ` Boqun Feng 2018-04-07 5:23 ` Boqun Feng 2018-04-05 16:59 ` [PATCH 09/10] locking/qspinlock: Make queued_spin_unlock use smp_store_release Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 16:59 ` [PATCH 10/10] locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb() Will Deacon 2018-04-05 16:59 ` Will Deacon 2018-04-05 17:28 ` Peter Zijlstra 2018-04-05 17:28 ` Peter Zijlstra 2018-04-06 11:34 ` Will Deacon 2018-04-06 11:34 ` Will Deacon 2018-04-06 13:05 ` Andrea Parri 2018-04-06 13:05 ` Andrea Parri 2018-04-06 15:27 ` Will Deacon 2018-04-06 15:27 ` Will Deacon 2018-04-06 15:49 ` Andrea Parri 2018-04-06 15:49 ` Andrea Parri 2018-04-07 5:47 ` Boqun Feng 2018-04-07 5:47 ` Boqun Feng 2018-04-09 10:47 ` Will Deacon 2018-04-09 10:47 ` Will Deacon 2018-04-06 13:22 ` [PATCH 00/10] kernel/locking: qspinlock improvements Andrea Parri 2018-04-06 13:22 ` Andrea Parri 2018-04-11 10:20 ` Catalin Marinas 2018-04-11 10:20 ` Catalin Marinas 2018-04-11 15:39 ` Andrea Parri 2018-04-11 15:39 ` Andrea Parri
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