[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH v10 09/19] qspinlock: Prepare for unfair lock support

On 05/08/2014 03:06 PM, Peter Zijlstra wrote:
On Wed, May 07, 2014 at 11:01:37AM -0400, Waiman Long wrote:
If unfair lock is supported, the lock acquisition loop at the end of
the queue_spin_lock_slowpath() function may need to detect the fact
the lock can be stolen. Code are added for the stolen lock detection.

A new qhead macro is also defined as a shorthand for mcs.locked.
NAK, unfair should be a pure test-and-set lock.

I have performance data showing that a simple test-and-set lock does not scale well. That is the primary reason of ditching the test-and-set lock and use a more complicated scheme which scales better. Also, it will be hard to make the unfair test-and-set lock code to coexist nicely with PV spinlock code.

   * get_qlock - Set the lock bit and own the lock
- * @lock: Pointer to queue spinlock structure
+ * @lock : Pointer to queue spinlock structure
+ * Return: 1 if lock acquired, 0 otherwise
   * This routine should only be called when the caller is the only one
   * entitled to acquire the lock.
-static __always_inline void get_qlock(struct qspinlock *lock)
+static __always_inline int get_qlock(struct qspinlock *lock)
        struct __qspinlock *l = (void *)lock;

        ACCESS_ONCE(l->locked) = _Q_LOCKED_VAL;
+       return 1;
and here you make a horribly named function more horrible;
try_set_locked() is that its now.

Will do.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.