[dpdk-dev] [PATCH v3 2/2] mempool/nb_stack: add non-blocking stack mempool

[Gage Eads]

This commit adds support for non-blocking (linked list based) stack mempool
handler. The stack uses a 128-bit compare-and-swap instruction, and thus is
limited to x86_64. The 128-bit CAS atomically updates the stack top pointer
and a modification counter, which protects against the ABA problem.

In mempool_perf_autotest the lock-based stack outperforms the non-blocking
handler*, however:
- For applications with preemptible pthreads, a lock-based stack's
  worst-case performance (i.e. one thread being preempted while
  holding the spinlock) is much worse than the non-blocking stack's.
- Using per-thread mempool caches will largely mitigate the performance
  difference.

*Test setup: x86_64 build with default config, dual-socket Xeon E5-2699 v4,
running on isolcpus cores with a tickless scheduler. The lock-based stack's
rate_persec was 1x-3.5x the non-blocking stack's.

Signed-off-by: Gage Eads <gage.eads at intel.com>
Acked-by: Andrew Rybchenko <arybchenko at solarflare.com>
---
 MAINTAINERS                                        |   4 +
 config/common_base                                 |   1 +
 doc/guides/prog_guide/env_abstraction_layer.rst    |   5 +
 drivers/mempool/Makefile                           |   3 +
 drivers/mempool/meson.build                        |   3 +-
 drivers/mempool/nb_stack/Makefile                  |  23 ++++
 drivers/mempool/nb_stack/meson.build               |   8 ++
 drivers/mempool/nb_stack/nb_lifo.h                 | 147 +++++++++++++++++++++
 drivers/mempool/nb_stack/rte_mempool_nb_stack.c    | 125 ++++++++++++++++++
 .../nb_stack/rte_mempool_nb_stack_version.map      |   4 +
 mk/rte.app.mk                                      |   7 +-
 11 files changed, 327 insertions(+), 3 deletions(-)
 create mode 100644 drivers/mempool/nb_stack/Makefile
 create mode 100644 drivers/mempool/nb_stack/meson.build
 create mode 100644 drivers/mempool/nb_stack/nb_lifo.h
 create mode 100644 drivers/mempool/nb_stack/rte_mempool_nb_stack.c
 create mode 100644 drivers/mempool/nb_stack/rte_mempool_nb_stack_version.map

diff --git a/MAINTAINERS b/MAINTAINERS
index 470f36b9c..5519d3323 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -416,6 +416,10 @@ M: Artem V. Andreev <artem.andreev at oktetlabs.ru>
 M: Andrew Rybchenko <arybchenko at solarflare.com>
 F: drivers/mempool/bucket/
 
+Non-blocking stack memory pool
+M: Gage Eads <gage.eads at intel.com>
+F: drivers/mempool/nb_stack/
+
 
 Bus Drivers
 -----------
diff --git a/config/common_base b/config/common_base
index 964a6956e..8a51f36b1 100644
--- a/config/common_base
+++ b/config/common_base
@@ -726,6 +726,7 @@ CONFIG_RTE_LIBRTE_MEMPOOL_DEBUG=n
 #
 CONFIG_RTE_DRIVER_MEMPOOL_BUCKET=y
 CONFIG_RTE_DRIVER_MEMPOOL_BUCKET_SIZE_KB=64
+CONFIG_RTE_DRIVER_MEMPOOL_NB_STACK=y
 CONFIG_RTE_DRIVER_MEMPOOL_RING=y
 CONFIG_RTE_DRIVER_MEMPOOL_STACK=y
 
diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index 929d76dba..9497b879c 100644
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -541,6 +541,11 @@ Known Issues
 
   5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
 
+  Alternatively, x86_64 applications can use the non-blocking stack mempool handler. When considering this handler, note that:
+
+  - it is limited to the x86_64 platform, because it uses an instruction (16-byte compare-and-swap) that is not available on other platforms.
+  - it has worse average-case performance than the non-preemptive rte_ring, but software caching (e.g. the mempool cache) can mitigate this by reducing the number of handler operations.
+
 + rte_timer
 
   Running  ``rte_timer_manage()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed.
diff --git a/drivers/mempool/Makefile b/drivers/mempool/Makefile
index 28c2e8360..895cf8a34 100644
--- a/drivers/mempool/Makefile
+++ b/drivers/mempool/Makefile
@@ -10,6 +10,9 @@ endif
 ifeq ($(CONFIG_RTE_EAL_VFIO)$(CONFIG_RTE_LIBRTE_FSLMC_BUS),yy)
 DIRS-$(CONFIG_RTE_LIBRTE_DPAA2_MEMPOOL) += dpaa2
 endif
+ifeq ($(CONFIG_RTE_ARCH_X86_64),y)
+DIRS-$(CONFIG_RTE_DRIVER_MEMPOOL_NB_STACK) += nb_stack
+endif
 DIRS-$(CONFIG_RTE_DRIVER_MEMPOOL_RING) += ring
 DIRS-$(CONFIG_RTE_DRIVER_MEMPOOL_STACK) += stack
 DIRS-$(CONFIG_RTE_LIBRTE_OCTEONTX_MEMPOOL) += octeontx
diff --git a/drivers/mempool/meson.build b/drivers/mempool/meson.build
index 4527d9806..220cfaf63 100644
--- a/drivers/mempool/meson.build
+++ b/drivers/mempool/meson.build
@@ -1,7 +1,8 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # Copyright(c) 2017 Intel Corporation
 
-drivers = ['bucket', 'dpaa', 'dpaa2', 'octeontx', 'ring', 'stack']
+drivers = ['bucket', 'dpaa', 'dpaa2', 'nb_stack', 'octeontx', 'ring', 'stack']
+
 std_deps = ['mempool']
 config_flag_fmt = 'RTE_LIBRTE_ at 0@_MEMPOOL'
 driver_name_fmt = 'rte_mempool_ at 0@'
diff --git a/drivers/mempool/nb_stack/Makefile b/drivers/mempool/nb_stack/Makefile
new file mode 100644
index 000000000..318b18283
--- /dev/null
+++ b/drivers/mempool/nb_stack/Makefile
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2019 Intel Corporation
+
+include $(RTE_SDK)/mk/rte.vars.mk
+
+#
+# library name
+#
+LIB = librte_mempool_nb_stack.a
+
+CFLAGS += -O3
+CFLAGS += $(WERROR_FLAGS)
+
+# Headers
+LDLIBS += -lrte_eal -lrte_mempool
+
+EXPORT_MAP := rte_mempool_nb_stack_version.map
+
+LIBABIVER := 1
+
+SRCS-$(CONFIG_RTE_DRIVER_MEMPOOL_NB_STACK) += rte_mempool_nb_stack.c
+
+include $(RTE_SDK)/mk/rte.lib.mk
diff --git a/drivers/mempool/nb_stack/meson.build b/drivers/mempool/nb_stack/meson.build
new file mode 100644
index 000000000..4a699511d
--- /dev/null
+++ b/drivers/mempool/nb_stack/meson.build
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright(c) 2019 Intel Corporation
+
+if arch_subdir != 'x86' or cc.sizeof('void *') == 4
+	build = false
+endif
+
+sources = files('rte_mempool_nb_stack.c')
diff --git a/drivers/mempool/nb_stack/nb_lifo.h b/drivers/mempool/nb_stack/nb_lifo.h
new file mode 100644
index 000000000..ad4a3401f
--- /dev/null
+++ b/drivers/mempool/nb_stack/nb_lifo.h
@@ -0,0 +1,147 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2019 Intel Corporation
+ */
+
+#ifndef _NB_LIFO_H_
+#define _NB_LIFO_H_
+
+struct nb_lifo_elem {
+	void *data;
+	struct nb_lifo_elem *next;
+};
+
+struct nb_lifo_head {
+	struct nb_lifo_elem *top; /**< Stack top */
+	uint64_t cnt; /**< Modification counter */
+};
+
+struct nb_lifo {
+	volatile struct nb_lifo_head head __rte_aligned(16);
+	rte_atomic64_t len;
+} __rte_cache_aligned;
+
+static __rte_always_inline void
+nb_lifo_init(struct nb_lifo *lifo)
+{
+	memset(lifo, 0, sizeof(*lifo));
+	rte_atomic64_set(&lifo->len, 0);
+}
+
+static __rte_always_inline unsigned int
+nb_lifo_len(struct nb_lifo *lifo)
+{
+	/* nb_lifo_push() and nb_lifo_pop() do not update the list's contents
+	 * and lifo->len atomically, which can cause the list to appear shorter
+	 * than it actually is if this function is called while other threads
+	 * are modifying the list.
+	 *
+	 * However, given the inherently approximate nature of the get_count
+	 * callback -- even if the list and its size were updated atomically,
+	 * the size could change between when get_count executes and when the
+	 * value is returned to the caller -- this is acceptable.
+	 *
+	 * The lifo->len updates are placed such that the list may appear to
+	 * have fewer elements than it does, but will never appear to have more
+	 * elements. If the mempool is near-empty to the point that this is a
+	 * concern, the user should consider increasing the mempool size.
+	 */
+	return (unsigned int)rte_atomic64_read(&lifo->len);
+}
+
+static __rte_always_inline void
+nb_lifo_push(struct nb_lifo *lifo,
+	     struct nb_lifo_elem *first,
+	     struct nb_lifo_elem *last,
+	     unsigned int num)
+{
+	while (1) {
+		struct nb_lifo_head old_head, new_head;
+
+		old_head = lifo->head;
+
+		/* Swing the top pointer to the first element in the list and
+		 * make the last element point to the old top.
+		 */
+		new_head.top = first;
+		new_head.cnt = old_head.cnt + 1;
+
+		last->next = old_head.top;
+
+		if (rte_atomic128_cmpset((volatile uint64_t *)&lifo->head,
+					 (uint64_t *)&old_head,
+					 (uint64_t *)&new_head))
+			break;
+	}
+
+	rte_atomic64_add(&lifo->len, num);
+}
+
+static __rte_always_inline void
+nb_lifo_push_single(struct nb_lifo *lifo, struct nb_lifo_elem *elem)
+{
+	nb_lifo_push(lifo, elem, elem, 1);
+}
+
+static __rte_always_inline struct nb_lifo_elem *
+nb_lifo_pop(struct nb_lifo *lifo,
+	    unsigned int num,
+	    void **obj_table,
+	    struct nb_lifo_elem **last)
+{
+	struct nb_lifo_head old_head;
+
+	/* Reserve num elements, if available */
+	while (1) {
+		uint64_t len = rte_atomic64_read(&lifo->len);
+
+		/* Does the list contain enough elements? */
+		if (len < num)
+			return NULL;
+
+		if (rte_atomic64_cmpset((volatile uint64_t *)&lifo->len,
+					len, len - num))
+			break;
+	}
+
+	/* Pop num elements */
+	while (1) {
+		struct nb_lifo_head new_head;
+		struct nb_lifo_elem *tmp;
+		unsigned int i;
+
+		old_head = lifo->head;
+
+		tmp = old_head.top;
+
+		/* Traverse the list to find the new head. A next pointer will
+		 * either point to another element or NULL; if a thread
+		 * encounters a pointer that has already been popped, the CAS
+		 * will fail.
+		 */
+		for (i = 0; i < num && tmp != NULL; i++) {
+			if (obj_table)
+				obj_table[i] = tmp->data;
+			if (last)
+				*last = tmp;
+			tmp = tmp->next;
+		}
+
+		/* If NULL was encountered, the list was modified while
+		 * traversing it. Retry.
+		 */
+		if (i != num)
+			continue;
+
+		new_head.top = tmp;
+		new_head.cnt = old_head.cnt + 1;
+
+		if (rte_atomic128_cmpset((volatile uint64_t *)&lifo->head,
+					 (uint64_t *)&old_head,
+					 (uint64_t *)&new_head))
+			break;
+	}
+
+	return old_head.top;
+}
+
+#endif /* _NB_LIFO_H_ */
diff --git a/drivers/mempool/nb_stack/rte_mempool_nb_stack.c b/drivers/mempool/nb_stack/rte_mempool_nb_stack.c
new file mode 100644
index 000000000..1818a2cfa
--- /dev/null
+++ b/drivers/mempool/nb_stack/rte_mempool_nb_stack.c
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2019 Intel Corporation
+ */
+
+#include <stdio.h>
+#include <rte_mempool.h>
+#include <rte_malloc.h>
+
+#include "nb_lifo.h"
+
+struct rte_mempool_nb_stack {
+	uint64_t size;
+	struct nb_lifo used_lifo; /**< LIFO containing mempool pointers  */
+	struct nb_lifo free_lifo; /**< LIFO containing unused LIFO elements */
+};
+
+static int
+nb_stack_alloc(struct rte_mempool *mp)
+{
+	struct rte_mempool_nb_stack *s;
+	struct nb_lifo_elem *elems;
+	unsigned int n = mp->size;
+	unsigned int size, i;
+
+	size = sizeof(*s) + n * sizeof(struct nb_lifo_elem);
+
+	/* Allocate our local memory structure */
+	s = rte_zmalloc_socket("mempool-nb_stack",
+			       size,
+			       RTE_CACHE_LINE_SIZE,
+			       mp->socket_id);
+	if (s == NULL) {
+		RTE_LOG(ERR, MEMPOOL, "Cannot allocate nb_stack!\n");
+		return -ENOMEM;
+	}
+
+	s->size = n;
+
+	nb_lifo_init(&s->used_lifo);
+	nb_lifo_init(&s->free_lifo);
+
+	elems = (struct nb_lifo_elem *)&s[1];
+	for (i = 0; i < n; i++)
+		nb_lifo_push_single(&s->free_lifo, &elems[i]);
+
+	mp->pool_data = s;
+
+	return 0;
+}
+
+static int
+nb_stack_enqueue(struct rte_mempool *mp, void * const *obj_table,
+		 unsigned int n)
+{
+	struct rte_mempool_nb_stack *s = mp->pool_data;
+	struct nb_lifo_elem *first, *last, *tmp;
+	unsigned int i;
+
+	if (unlikely(n == 0))
+		return 0;
+
+	/* Pop n free elements */
+	first = nb_lifo_pop(&s->free_lifo, n, NULL, NULL);
+	if (unlikely(first == NULL))
+		return -ENOBUFS;
+
+	/* Prepare the list elements */
+	tmp = first;
+	for (i = 0; i < n; i++) {
+		tmp->data = obj_table[i];
+		last = tmp;
+		tmp = tmp->next;
+	}
+
+	/* Enqueue them to the used list */
+	nb_lifo_push(&s->used_lifo, first, last, n);
+
+	return 0;
+}
+
+static int
+nb_stack_dequeue(struct rte_mempool *mp, void **obj_table,
+		 unsigned int n)
+{
+	struct rte_mempool_nb_stack *s = mp->pool_data;
+	struct nb_lifo_elem *first, *last;
+
+	if (unlikely(n == 0))
+		return 0;
+
+	/* Pop n used elements */
+	first = nb_lifo_pop(&s->used_lifo, n, obj_table, &last);
+	if (unlikely(first == NULL))
+		return -ENOENT;
+
+	/* Enqueue the list elements to the free list */
+	nb_lifo_push(&s->free_lifo, first, last, n);
+
+	return 0;
+}
+
+static unsigned
+nb_stack_get_count(const struct rte_mempool *mp)
+{
+	struct rte_mempool_nb_stack *s = mp->pool_data;
+
+	return nb_lifo_len(&s->used_lifo);
+}
+
+static void
+nb_stack_free(struct rte_mempool *mp)
+{
+	rte_free(mp->pool_data);
+}
+
+static struct rte_mempool_ops ops_nb_stack = {
+	.name = "nb_stack",
+	.alloc = nb_stack_alloc,
+	.free = nb_stack_free,
+	.enqueue = nb_stack_enqueue,
+	.dequeue = nb_stack_dequeue,
+	.get_count = nb_stack_get_count
+};
+
+MEMPOOL_REGISTER_OPS(ops_nb_stack);
diff --git a/drivers/mempool/nb_stack/rte_mempool_nb_stack_version.map b/drivers/mempool/nb_stack/rte_mempool_nb_stack_version.map
new file mode 100644
index 000000000..fc8c95e91
--- /dev/null
+++ b/drivers/mempool/nb_stack/rte_mempool_nb_stack_version.map
@@ -0,0 +1,4 @@
+DPDK_19.05 {
+
+	local: *;
+};
diff --git a/mk/rte.app.mk b/mk/rte.app.mk
index 02e8b6f05..d4b4aaaf6 100644
--- a/mk/rte.app.mk
+++ b/mk/rte.app.mk
@@ -131,8 +131,11 @@ endif
 ifeq ($(CONFIG_RTE_BUILD_SHARED_LIB),n)
 # plugins (link only if static libraries)
 
-_LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_BUCKET) += -lrte_mempool_bucket
-_LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_STACK)  += -lrte_mempool_stack
+_LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_BUCKET)   += -lrte_mempool_bucket
+ifeq ($(CONFIG_RTE_ARCH_X86_64),y)
+_LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_NB_STACK) += -lrte_mempool_nb_stack
+endif
+_LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_STACK)    += -lrte_mempool_stack
 ifeq ($(CONFIG_RTE_LIBRTE_DPAA_BUS),y)
 _LDLIBS-$(CONFIG_RTE_LIBRTE_DPAA_MEMPOOL)   += -lrte_mempool_dpaa
 endif
-- 
2.13.6