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Re: [Xen-devel] [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock

On 03/02/2014 09:10 AM, Oleg Nesterov wrote:
On 02/26, Waiman Long wrote:
+ * x86-64 specific queue spinlock union structure
+ */
+union arch_qspinlock {
+       struct qspinlock slock;
+       u8               lock;  /* Lock bit     */
And this enables the optimized version of queue_spin_setlock().

But why does it check ACCESS_ONCE(qlock->lock) == 0 ? This is called
right after queue_get_lock_qcode() returns 0, this locked should be
likely unlocked.


Yes, the read check in queue_spin_setlock is probably redundant. Will remove that.


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