diff options
| author | Will Deacon <will.deacon@arm.com> | 2018-04-26 11:34:23 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-04-27 09:48:50 +0200 |
| commit | c131a198c497db436b558ac5e9a140cdcb91b304 (patch) | |
| tree | 9f213e959da1d64f45dd7748f94c9d7146d888d4 /kernel/locking | |
| parent | 7f56b58a92aaf2cab049f32a19af7cc57a3972f2 (diff) | |
| download | linux-0-day-c131a198c497db436b558ac5e9a140cdcb91b304.tar.gz linux-0-day-c131a198c497db436b558ac5e9a140cdcb91b304.tar.xz | |
locking/qspinlock: Use smp_cond_load_relaxed() to wait for next node
When a locker reaches the head of the queue and takes the lock, a
concurrent locker may enqueue and force the lock holder to spin
whilst its node->next field is initialised. Rather than open-code
a READ_ONCE/cpu_relax() loop, this can be implemented using
smp_cond_load_relaxed() instead.
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/1524738868-31318-10-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/qspinlock.c | 6 |
1 files changed, 2 insertions, 4 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 56af1fa9874d8..d6c3b029bd935 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -483,10 +483,8 @@ locked: /* * contended path; wait for next if not observed yet, release. */ - if (!next) { - while (!(next = READ_ONCE(node->next))) - cpu_relax(); - } + if (!next) + next = smp_cond_load_relaxed(&node->next, (VAL)); arch_mcs_spin_unlock_contended(&next->locked); pv_kick_node(lock, next); |