[PATCH v6 0/3] skb_array: array based FIFO for skbs

@@ -0,0 +1,267 @@
+/*
+ *	Definitions for the 'struct ptr_ring' datastructure.
+ *
+ *	Author:
+ *		Michael S. Tsirkin <mst@redhat.com>
+ *
+ *	Copyright (C) 2016 Red Hat, Inc.
+ *
+ *	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 pointers 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_PTR_RING_H
+#define _LINUX_PTR_RING_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 ptr_ring {
+	int producer ____cacheline_aligned_in_smp;
+	spinlock_t producer_lock;
+	int consumer ____cacheline_aligned_in_smp;
+	spinlock_t consumer_lock;
+	/* Shared consumer/producer data */
+	/* Read-only by both the producer and the consumer */
+	int size ____cacheline_aligned_in_smp; /* max entries in queue */
+	void **queue;
+};
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax().
+ * Callers don't need to take producer lock - if they don't
+ * the next call to __ptr_ring_produce may fail.
+ */
+static inline bool __ptr_ring_full(struct ptr_ring *r)
+{
+	return r->queue[r->producer];
+}
+
+static inline bool ptr_ring_full(struct ptr_ring *r)
+{
+	barrier();
+	return __ptr_ring_full(r);
+}
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax().
+ */
+static inline int __ptr_ring_produce(struct ptr_ring *r, void *ptr)
+{
+	if (__ptr_ring_full(r))
+		return -ENOSPC;
+
+	r->queue[r->producer++] = ptr;
+	if (unlikely(r->producer >= r->size))
+		r->producer = 0;
+	return 0;
+}
+
+static inline int ptr_ring_produce(struct ptr_ring *r, void *ptr)
+{
+	int ret;
+
+	spin_lock(&r->producer_lock);
+	ret = __ptr_ring_produce(r, ptr);
+	spin_unlock(&r->producer_lock);
+
+	return ret;
+}
+
+static inline int ptr_ring_produce_irq(struct ptr_ring *r, void *ptr)
+{
+	int ret;
+
+	spin_lock_irq(&r->producer_lock);
+	ret = __ptr_ring_produce(r, ptr);
+	spin_unlock_irq(&r->producer_lock);
+
+	return ret;
+}
+
+static inline int ptr_ring_produce_any(struct ptr_ring *r, void *ptr)
+{
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&r->producer_lock, flags);
+	ret = __ptr_ring_produce(r, ptr);
+	spin_unlock_irqrestore(&r->producer_lock, flags);
+
+	return ret;
+}
+
+static inline int ptr_ring_produce_bh(struct ptr_ring *r, void *ptr)
+{
+	int ret;
+
+	spin_lock_bh(&r->producer_lock);
+	ret = __ptr_ring_produce(r, ptr);
+	spin_unlock_bh(&r->producer_lock);
+
+	return ret;
+}
+
+/* Note: callers invoking this in a loop must use a compiler barrier,
+ * for example cpu_relax(). Callers must take consumer_lock
+ * if they dereference the pointer - see e.g. PTR_RING_PEEK_FIELD.
+ * There's no need for a lock if pointer is merely tested - see e.g.
+ * ptr_ring_empty.
+ */
+static inline void *__ptr_ring_peek(struct ptr_ring *r)
+{
+	return r->queue[r->consumer];
+}
+
+static inline bool ptr_ring_empty(struct ptr_ring *r)
+{
+	barrier();
+	return !__ptr_ring_peek(r);
+}
+
+/* Must only be called after __ptr_ring_peek returned !NULL */
+static inline void __ptr_ring_discard_one(struct ptr_ring *r)
+{
+	r->queue[r->consumer++] = NULL;
+	if (unlikely(r->consumer >= r->size))
+		r->consumer = 0;
+}
+
+static inline void *__ptr_ring_consume(struct ptr_ring *r)
+{
+	void *ptr;
+
+	ptr = __ptr_ring_peek(r);
+	if (ptr)
+		__ptr_ring_discard_one(r);
+
+	return ptr;
+}
+
+static inline void *ptr_ring_consume(struct ptr_ring *r)
+{
+	void *ptr;
+
+	spin_lock(&r->consumer_lock);
+	ptr = __ptr_ring_consume(r);
+	spin_unlock(&r->consumer_lock);
+
+	return ptr;
+}
+
+static inline void *ptr_ring_consume_irq(struct ptr_ring *r)
+{
+	void *ptr;
+
+	spin_lock_irq(&r->consumer_lock);
+	ptr = __ptr_ring_consume(r);
+	spin_unlock_irq(&r->consumer_lock);
+
+	return ptr;
+}
+
+static inline void *ptr_ring_consume_any(struct ptr_ring *r)
+{
+	unsigned long flags;
+	void *ptr;
+
+	spin_lock_irqsave(&r->consumer_lock, flags);
+	ptr = __ptr_ring_consume(r);
+	spin_unlock_irqrestore(&r->consumer_lock, flags);
+
+	return ptr;
+}
+
+static inline void *ptr_ring_consume_bh(struct ptr_ring *r)
+{
+	void *ptr;
+
+	spin_lock(&r->consumer_lock);
+	ptr = __ptr_ring_consume(r);
+	spin_unlock(&r->consumer_lock);
+
+	return ptr;
+}
+
+/* Cast to structure type and peek at a field without discarding from FIFO.
+ * Callers must take consumer_lock.
+ */
+#define __PTR_RING_PEEK_FIELD(r, type, field, dflt) ({ \
+       type *__PTR_RING_PEEK_FIELD_p = __ptr_ring_peek(r); \
+	\
+       __PTR_RING_PEEK_FIELD_p ? __PTR_RING_PEEK_FIELD_p->field : (dflt); \
+})
+
+#define PTR_RING_PEEK_FIELD(r, type, field, dflt) ({ \
+	typeof(((type *)0)->field) __PTR_RING_PEEK_FIELD_v; \
+	\
+	spin_lock(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v = __PTR_RING_PEEK_FIELD(r, type, field, dflt); \
+	spin_unlock(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v; \
+})
+
+#define PTR_RING_PEEK_FIELD_IRQ(r, type, field, dflt) ({ \
+	typeof(((type *)0)->field) __PTR_RING_PEEK_FIELD_v; \
+	\
+	spin_lock_irq(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v = __PTR_RING_PEEK_FIELD(r, type, field, dflt); \
+	spin_unlock_irq(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v; \
+})
+
+#define PTR_RING_PEEK_FIELD_BH(r, type, field, dflt) ({ \
+	typeof(((type *)0)->field) __PTR_RING_PEEK_FIELD_v; \
+	\
+	spin_lock_bh(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v = __PTR_RING_PEEK_FIELD(r, type, field, dflt); \
+	spin_unlock_bh(&(r)->consumer_lock); \
+	__PTR_RING_PEEK_FIELD_v; \
+})
+
+#define PTR_RING_PEEK_FIELD_ANY(r, type, field, dflt) ({ \
+	typeof(((type *)0)->field) __PTR_RING_PEEK_FIELD_v; \
+	unsigned long __PTR_RING_PEEK_FIELD_f;\
+	\
+	spin_lock_irqsave(&(r)->consumer_lock, __PTR_RING_PEEK_FIELD_f); \
+	__PTR_RING_PEEK_FIELD_v = __PTR_RING_PEEK_FIELD(r, type, field, dflt); \
+	spin_unlock_irqrestore(&(r)->consumer_lock, __PTR_RING_PEEK_FIELD_f); \
+	__PTR_RING_PEEK_FIELD_v; \
+})
+
+static inline int ptr_ring_init(struct ptr_ring *r, int size, gfp_t gfp)
+{
+	r->queue = kzalloc(ALIGN(size * sizeof *(r->queue), SMP_CACHE_BYTES),
+			   gfp);
+	if (!r->queue)
+		return -ENOMEM;
+
+	r->size = size;
+	r->producer = r->consumer = 0;
+	spin_lock_init(&r->producer_lock);
+	spin_lock_init(&r->consumer_lock);
+
+	return 0;
+}
+
+static inline void ptr_ring_cleanup(struct ptr_ring *r)
+{
+	kfree(r->queue);
+}
+
+#endif /* _LINUX_PTR_RING_H  */

@@ -0,0 +1,192 @@
+#define _GNU_SOURCE
+#include "main.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <pthread.h>
+#include <malloc.h>
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+
+#define SMP_CACHE_BYTES 64
+#define cache_line_size() SMP_CACHE_BYTES
+#define ____cacheline_aligned_in_smp __attribute__ ((aligned (SMP_CACHE_BYTES)))
+#define unlikely(x)    (__builtin_expect(!!(x), 0))
+#define ALIGN(x, a) (((x) + (a) - 1) / (a) * (a))
+typedef pthread_spinlock_t  spinlock_t;
+
+typedef int gfp_t;
+static void *kzalloc(unsigned size, gfp_t gfp)
+{
+	void *p = memalign(64, size);
+	if (!p)
+		return p;
+	memset(p, 0, size);
+
+	return p;
+}
+
+static void kfree(void *p)
+{
+	if (p)
+		free(p);
+}
+
+static void spin_lock_init(spinlock_t *lock)
+{
+	int r = pthread_spin_init(lock, 0);
+	assert(!r);
+}
+
+static void spin_lock(spinlock_t *lock)
+{
+	int ret = pthread_spin_lock(lock);
+	assert(!ret);
+}
+
+static void spin_unlock(spinlock_t *lock)
+{
+	int ret = pthread_spin_unlock(lock);
+	assert(!ret);
+}
+
+static void spin_lock_bh(spinlock_t *lock)
+{
+	spin_lock(lock);
+}
+
+static void spin_unlock_bh(spinlock_t *lock)
+{
+	spin_unlock(lock);
+}
+
+static void spin_lock_irq(spinlock_t *lock)
+{
+	spin_lock(lock);
+}
+
+static void spin_unlock_irq(spinlock_t *lock)
+{
+	spin_unlock(lock);
+}
+
+static void spin_lock_irqsave(spinlock_t *lock, unsigned long f)
+{
+	spin_lock(lock);
+}
+
+static void spin_unlock_irqrestore(spinlock_t *lock, unsigned long f)
+{
+	spin_unlock(lock);
+}
+
+#include "../../../include/linux/ptr_ring.h"
+
+static unsigned long long headcnt, tailcnt;
+static struct ptr_ring array ____cacheline_aligned_in_smp;
+
+/* implemented by ring */
+void alloc_ring(void)
+{
+	int ret = ptr_ring_init(&array, ring_size, 0);
+	assert(!ret);
+}
+
+/* guest side */
+int add_inbuf(unsigned len, void *buf, void *datap)
+{
+	int ret;
+
+	ret = __ptr_ring_produce(&array, buf);
+	if (ret >= 0) {
+		ret = 0;
+		headcnt++;
+	}
+
+	return ret;
+}
+
+/*
+ * ptr_ring API provides no way for producer to find out whether a given
+ * buffer was consumed.  Our tests merely require that a successful get_buf
+ * implies that add_inbuf succeed in the past, and that add_inbuf will succeed,
+ * fake it accordingly.
+ */
+void *get_buf(unsigned *lenp, void **bufp)
+{
+	void *datap;
+
+	if (tailcnt == headcnt || __ptr_ring_full(&array))
+		datap = NULL;
+	else {
+		datap = "Buffer\n";
+		++tailcnt;
+	}
+
+	return datap;
+}
+
+void poll_used(void)
+{
+	void *b;
+
+	do {
+		if (tailcnt == headcnt || __ptr_ring_full(&array)) {
+			b = NULL;
+			barrier();
+		} else {
+			b = "Buffer\n";
+		}
+	} while (!b);
+}
+
+void disable_call()
+{
+	assert(0);
+}
+
+bool enable_call()
+{
+	assert(0);
+}
+
+void kick_available(void)
+{
+	assert(0);
+}
+
+/* host side */
+void disable_kick()
+{
+	assert(0);
+}
+
+bool enable_kick()
+{
+	assert(0);
+}
+
+void poll_avail(void)
+{
+	void *b;
+
+	do {
+		barrier();
+		b = __ptr_ring_peek(&array);
+	} while (!b);
+}
+
+bool use_buf(unsigned *lenp, void **bufp)
+{
+	void *ptr;
+
+	ptr = __ptr_ring_consume(&array);
+
+	return ptr;
+}
+
+void call_used(void)
+{
+	assert(0);
+}

@@ -1,6 +1,6 @@
 all:
 
-all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder noring
+all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder ptr_ring noring
 
 CFLAGS += -Wall
 CFLAGS += -pthread -O2 -ggdb

@@ -8,6 +8,7 @@ LDFLAGS += -pthread -O2 -ggdb
 
 main.o: main.c main.h
 ring.o: ring.c main.h
+ptr_ring.o: ptr_ring.c main.h ../../../include/linux/ptr_ring.h
 virtio_ring_0_9.o: virtio_ring_0_9.c main.h
 virtio_ring_poll.o: virtio_ring_poll.c virtio_ring_0_9.c main.h
 virtio_ring_inorder.o: virtio_ring_inorder.c virtio_ring_0_9.c main.h

@@ -15,6 +16,7 @@ ring: ring.o main.o
 virtio_ring_0_9: virtio_ring_0_9.o main.o
 virtio_ring_poll: virtio_ring_poll.o main.o
 virtio_ring_inorder: virtio_ring_inorder.o main.o
+ptr_ring: ptr_ring.o main.o
 noring: noring.o main.o
 clean:
 	-rm main.o

@@ -22,6 +24,7 @@ clean:
 	-rm virtio_ring_0_9.o virtio_ring_0_9
 	-rm virtio_ring_poll.o virtio_ring_poll
 	-rm virtio_ring_inorder.o virtio_ring_inorder
+	-rm ptr_ring.o ptr_ring
 	-rm noring.o noring
 
 .PHONY: all clean

@@ -0,0 +1,129 @@
+/*
+ *	Definitions for the 'struct skb_array' datastructure.
+ *
+ *	Author:
+ *		Michael S. Tsirkin <mst@redhat.com>
+ *
+ *	Copyright (C) 2016 Red Hat, Inc.
+ *
+ *	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.
+ *
+ *	Limited-size FIFO of skbs. Can be used more or less whenever
+ *	sk_buff_head can be used, except you need to know the queue size in
+ *	advance.
+ *	Implemented as a type-safe wrapper around ptr_ring.
+ */
+
+#ifndef _LINUX_SKB_ARRAY_H
+#define _LINUX_SKB_ARRAY_H 1
+
+#ifdef __KERNEL__
+#include <linux/ptr_ring.h>
+#include <linux/skbuff.h>
+#endif
+
+struct skb_array {
+	struct ptr_ring ring;
+};
+
+/* Might be slightly faster than skb_array_full below, but 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 __ptr_ring_full(&a->ring);
+}
+
+static inline bool skb_array_full(struct skb_array *a)
+{
+	return ptr_ring_full(&a->ring);
+}
+
+static inline int skb_array_produce(struct skb_array *a, struct sk_buff *skb)
+{
+	return ptr_ring_produce(&a->ring, skb);
+}
+
+static inline int skb_array_produce_irq(struct skb_array *a, struct sk_buff *skb)
+{
+	return ptr_ring_produce_irq(&a->ring, skb);
+}
+
+static inline int skb_array_produce_bh(struct skb_array *a, struct sk_buff *skb)
+{
+	return ptr_ring_produce_bh(&a->ring, skb);
+}
+
+static inline int skb_array_produce_any(struct skb_array *a, struct sk_buff *skb)
+{
+	return ptr_ring_produce_any(&a->ring, skb);
+}
+
+/* Might be slightly faster than skb_array_empty below, but callers invoking
+ * this in a loop must take care to use a compiler barrier, for example
+ * cpu_relax().
+ */
+static inline bool __skb_array_empty(struct skb_array *a)
+{
+	return !__ptr_ring_peek(&a->ring);
+}
+
+static inline bool skb_array_empty(struct skb_array *a)
+{
+	return ptr_ring_empty(&a->ring);
+}
+
+static inline struct sk_buff *skb_array_consume(struct skb_array *a)
+{
+	return ptr_ring_consume(&a->ring);
+}
+
+static inline struct sk_buff *skb_array_consume_irq(struct skb_array *a)
+{
+	return ptr_ring_consume_irq(&a->ring);
+}
+
+static inline struct sk_buff *skb_array_consume_any(struct skb_array *a)
+{
+	return ptr_ring_consume_any(&a->ring);
+}
+
+static inline struct sk_buff *skb_array_consume_bh(struct skb_array *a)
+{
+	return ptr_ring_consume_bh(&a->ring);
+}
+
+static inline int skb_array_peek_len(struct skb_array *a)
+{
+	return PTR_RING_PEEK_FIELD(&a->ring, struct sk_buff, len, 0);
+}
+
+static inline int skb_array_peek_len_irq(struct skb_array *a)
+{
+	return PTR_RING_PEEK_FIELD_IRQ(&a->ring, struct sk_buff, len, 0);
+}
+
+static inline int skb_array_peek_len_bh(struct skb_array *a)
+{
+	return PTR_RING_PEEK_FIELD_BH(&a->ring, struct sk_buff, len, 0);
+}
+
+static inline int skb_array_peek_len_any(struct skb_array *a)
+{
+	return PTR_RING_PEEK_FIELD_ANY(&a->ring, struct sk_buff, len, 0);
+}
+
+static inline int skb_array_init(struct skb_array *a, int size, gfp_t gfp)
+{
+	return ptr_ring_init(&a->ring, size, gfp);
+}
+
+static inline void skb_array_cleanup(struct skb_array *a)
+{
+	ptr_ring_cleanup(&a->ring);
+}
+
+#endif /* _LINUX_SKB_ARRAY_H  */