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, longman@redhat.com,
will.deacon@arm.com
Subject: [PATCH v3 08/14] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop
Date: Thu, 26 Apr 2018 11:34:22 +0100 [thread overview]
Message-ID: <1524738868-31318-9-git-send-email-will.deacon@arm.com> (raw)
In-Reply-To: <1524738868-31318-1-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:[~2018-04-26 10:35 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-26 10:34 [PATCH v3 00/14] kernel/locking: qspinlock improvements Will Deacon
2018-04-26 10:34 ` [PATCH v3 01/14] barriers: Introduce smp_cond_load_relaxed and atomic_cond_read_relaxed Will Deacon
2018-04-27 9:36 ` [tip:locking/core] locking/barriers: Introduce smp_cond_load_relaxed() and atomic_cond_read_relaxed() tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 02/14] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-27 9:37 ` [tip:locking/core] locking/qspinlock: Merge 'struct __qspinlock' into 'struct qspinlock' tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 03/14] locking/qspinlock: Bound spinning on pending->locked transition in slowpath Will Deacon
2018-04-27 9:37 ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 04/14] locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound Will Deacon
2018-04-27 9:38 ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-26 15:53 ` Peter Zijlstra
2018-04-26 16:55 ` Will Deacon
2018-04-28 12:45 ` Peter Zijlstra
2018-04-30 8:53 ` Will Deacon
2018-04-26 20:16 ` Waiman Long
2018-04-27 10:16 ` Will Deacon
2018-04-27 11:01 ` [tip:locking/core] locking/qspinlock: Remove duplicate clear_pending() function from PV code tip-bot for Will Deacon
2018-04-27 13:09 ` [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Waiman Long
2018-04-27 9:39 ` [tip:locking/core] locking/qspinlock: Remove unbounded cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 06/14] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue Will Deacon
2018-04-27 9:39 ` [tip:locking/core] locking/qspinlock: Kill cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 07/14] locking/qspinlock: Use atomic_cond_read_acquire Will Deacon
2018-04-27 9:40 ` [tip:locking/core] locking/qspinlock: Use atomic_cond_read_acquire() tip-bot for Will Deacon
2018-04-26 10:34 ` Will Deacon [this message]
2018-04-27 9:40 ` [tip:locking/core] locking/mcs: Use smp_cond_load_acquire() in MCS spin loop tip-bot for Jason Low
2018-04-26 10:34 ` [PATCH v3 09/14] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Will Deacon
2018-04-27 9:41 ` [tip:locking/core] locking/qspinlock: Use smp_cond_load_relaxed() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 10/14] locking/qspinlock: Make queued_spin_unlock use smp_store_release Will Deacon
2018-04-27 9:42 ` [tip:locking/core] locking/qspinlock: Use smp_store_release() in queued_spin_unlock() tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 11/14] locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb() Will Deacon
2018-04-27 9:42 ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 12/14] locking/qspinlock: Use try_cmpxchg instead of cmpxchg when locking Will Deacon
2018-04-27 9:43 ` [tip:locking/core] locking/qspinlock: Use try_cmpxchg() instead of cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 13/14] locking/qspinlock: Add stat tracking for pending vs slowpath Will Deacon
2018-04-27 9:43 ` [tip:locking/core] locking/qspinlock: Add stat tracking for pending vs. slowpath tip-bot for Waiman Long
2018-04-26 10:34 ` [PATCH v3 14/14] MAINTAINERS: Add myself as a co-maintainer for LOCKING PRIMITIVES Will Deacon
2018-04-26 15:55 ` Peter Zijlstra
2018-04-27 9:44 ` [tip:locking/core] MAINTAINERS: Add myself as a co-maintainer for the locking subsystem tip-bot for Will Deacon
2018-04-26 15:54 ` [PATCH v3 00/14] kernel/locking: qspinlock improvements Peter Zijlstra
2018-04-27 9:33 ` Ingo Molnar
2018-04-26 20:18 ` Waiman Long
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