Re: [PATCH v4 1/3] qspinlock: Introducing a 4-byte queue spinlock implementation

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On 02/18/2014 02:30 AM, Peter Zijlstra wrote:
On Mon, Feb 17, 2014 at 03:41:22PM -0500, Waiman Long wrote:
+/*
+ * The queue node structure
+ *
+ * This structure is essentially the same as the mcs_spinlock structure
+ * in mcs_spinlock.h file. This structure is retained for future extension
+ * where new fields may be added.
+ */
+struct qnode {
+	u32		 wait;		/* Waiting flag		*/
+	struct qnode	*next;		/* Next queue node addr */
+};
+
+struct qnode_set {
+	int		node_idx;	/* Current node to use */
+	struct qnode	nodes[MAX_QNODES];
+};
+
+/*
+ * Per-CPU queue node structures
+ */
+static DEFINE_PER_CPU(struct qnode_set, qnset) ____cacheline_aligned
+	= { 0 };
You really didn't pay attention did you.

That should be DEFINE_PER_CPU_ALIGNED()

Furthermore, your structure is bigger than 1 cacheline; your struct
qnode is 16 bytes, 4*16=64, and then you add that int.

Thank for letting me know about that. This is a minor problem that I will fix in the next version.

-Longman
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