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| author | Will Deacon <will.deacon@arm.com> | 2018-04-26 12:34:25 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-04-27 09:48:52 +0200 |
| commit | 9d4646d14d51d62b967a12452c30ea7edf8dd8fa (patch) | |
| tree | 9867a52f6c68760063540e8344ebd340bd66eeba /kernel/locking/mcs_spinlock.h | |
| parent | locking/qspinlock: Use smp_store_release() in queued_spin_unlock() (diff) | |
| download | linux-9d4646d14d51d62b967a12452c30ea7edf8dd8fa.tar.xz linux-9d4646d14d51d62b967a12452c30ea7edf8dd8fa.zip | |
locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb()
The qspinlock slowpath must ensure that the MCS node is fully initialised
before it can be reached by another other CPU. This is currently enforced
by using a RELEASE operation when updating the tail and also when linking
the node into the waitqueue, since the control dependency off xchg_tail
is insufficient to enforce sufficient ordering, see:
95bcade33a8a ("locking/qspinlock: Ensure node is initialised before updating prev->next")
Back-to-back RELEASE operations may be expensive on some architectures,
particularly those that implement them using fences under the hood. We
can replace the two RELEASE operations with a single smp_wmb() fence and
use RELAXED operations for the subsequent publishing of the node.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-12-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/mcs_spinlock.h')
0 files changed, 0 insertions, 0 deletions