[PATCH v5 1/2] skb_array: array based FIFO for skbs

["Michael S. Tsirkin" <mst@redhat.com>]

A simple array based FIFO of pointers.  Intended for net stack so uses
skbs for type safety, but we can replace with with void * if others find
it useful outside of net stack.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/linux/skb_array.h | 127 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 include/linux/skb_array.h

diff --git a/include/linux/skb_array.h b/include/linux/skb_array.h
new file mode 100644
index 0000000..d2535ad
--- /dev/null
+++ b/include/linux/skb_array.h
@@ -0,0 +1,127 @@
+/*
+ *	Author:
+ *		Michael S. Tsirkin <mst@redhat.com>
+ *
+ *	This program is free software; you can redistribute it and/or modify it
+ *	under the terms of the GNU General Public License as published by the
+ *	Free Software Foundation; either version 2 of the License, or (at your
+ *	option) any later version.
+ *
+ *	This is a limited-size FIFO maintaining sk_buff structures in FIFO
+ *	order, with one CPU producing entries and another consuming entries
+ *	from a FIFO.
+ *
+ *	This implementation tries to minimize cache-contention when there is a
+ *	single producer and a single consumer CPU.
+ */
+
+#ifndef _LINUX_SKB_ARRAY_H
+#define _LINUX_SKB_ARRAY_H 1
+
+#ifdef __KERNEL__
+#include <linux/spinlock.h>
+#include <linux/cache.h>
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <linux/cache.h>
+#include <linux/slab.h>
+#include <asm/errno.h>
+#endif
+
+struct sk_buff;
+
+struct skb_array {
+	int producer ____cacheline_aligned_in_smp;
+	spinlock_t producer_lock;
+	int consumer ____cacheline_aligned_in_smp;
+	spinlock_t consumer_lock;
+	/* Shared consumer/producer data */
+	int size ____cacheline_aligned_in_smp; /* max entries in queue */
+	struct sk_buff **queue;
+};
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax().
+ */
+static inline bool __skb_array_full(struct skb_array *a)
+{
+	return a->queue[a->producer];
+}
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax().
+ */
+static inline int __skb_array_produce(struct skb_array *a,
+				       struct sk_buff *skb)
+{
+	if (__skb_array_full(a))
+		return -ENOSPC;
+
+	a->queue[a->producer++] = skb;
+	if (unlikely(a->producer >= a->size))
+		a->producer = 0;
+	return 0;
+}
+
+static inline int skb_array_produce_bh(struct skb_array *a,
+				       struct sk_buff *skb)
+{
+	int ret;
+
+	spin_lock_bh(&a->producer_lock);
+	ret = __skb_array_produce(a, skb);
+	spin_unlock_bh(&a->producer_lock);
+
+	return ret;
+}
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax().
+ */
+static inline struct sk_buff *__skb_array_peek(struct skb_array *a)
+{
+	return a->queue[a->consumer];
+}
+
+/* Must only be called after __skb_array_peek returned !NULL */
+static inline void __skb_array_consume(struct skb_array *a)
+{
+	a->queue[a->consumer++] = NULL;
+	if (unlikely(a->consumer >= a->size))
+		a->consumer = 0;
+}
+
+static inline struct sk_buff *skb_array_consume_bh(struct skb_array *a)
+{
+	struct sk_buff *skb;
+
+	spin_lock_bh(&a->consumer_lock);
+	skb = __skb_array_peek(a);
+	if (skb)
+		__skb_array_consume(a);
+	spin_unlock_bh(&a->consumer_lock);
+
+	return skb;
+}
+
+static inline int skb_array_init(struct skb_array *a, int size, gfp_t gfp)
+{
+	a->queue = kzalloc(ALIGN(size * sizeof *(a->queue), SMP_CACHE_BYTES),
+			   gfp);
+	if (!a->queue)
+		return -ENOMEM;
+
+	a->size = size;
+	a->producer = a->consumer = 0;
+	spin_lock_init(&a->producer_lock);
+	spin_lock_init(&a->consumer_lock);
+
+	return 0;
+}
+
+static inline void skb_array_cleanup(struct skb_array *a)
+{
+	kfree(a->queue);
+}
+
+#endif /* _LINUX_SKB_ARRAY_H  */
-- 
MST