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| author | Peter Zijlstra <peterz@infradead.org> | 2015-09-04 17:25:23 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-09-11 07:49:42 +0200 |
| commit | 43b3f02899f74ae9914a39547cc5492156f0027a (patch) | |
| tree | 0db5018c95f8d243b974f42abda1c0c618abeee5 /kernel/locking/qspinlock.c | |
| parent | edcd591c77a48da753456f92daf8bb50fe9bac93 (diff) | |
| download | lwn-43b3f02899f74ae9914a39547cc5492156f0027a.tar.gz lwn-43b3f02899f74ae9914a39547cc5492156f0027a.zip | |
locking/qspinlock/x86: Fix performance regression under unaccelerated VMs
Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS
set and Linus noted that the test-and-set implementation was retarded.
One should spin on the variable with a load, not a RMW.
While there, remove 'queued' from the name, as the lock isn't queued
at all, but a simple test-and-set.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Dave Chinner <david@fromorbit.com>
Tested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: stable@vger.kernel.org # v4.2+
Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/qspinlock.c')
| -rw-r--r-- | kernel/locking/qspinlock.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 337c8818541d..87e9ce6a63c5 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) if (pv_enabled()) goto queue; - if (virt_queued_spin_lock(lock)) + if (virt_spin_lock(lock)) return; /* |