core: implement a global thread pool

This patch implements a thread pool that is wait-free for adding jobs to
the queue and uses a very small locked region to get jobs. This makes it
possible to decrease contention drastically. It's based on wfcqueue
structure provided by urcu library.

It automatically enables more threads when load demands it, and stops
them when not needed. There's a maximum number of threads that can be
used. This value can be configured.

Depending on the workload, the maximum number of threads plays an
important role. So it needs to be configured for optimal performance.
Currently the thread pool doesn't self adjust the maximum for the
workload, so this configuration needs to be changed manually.

For this reason, the global thread pool has been made optional, so that
volumes can still use the thread pool provided by io-threads.

To enable it for bricks, the following option needs to be set:

   config.global-threading = on

This option has no effect if bricks are already running. A restart is
required to activate it. It's recommended to also enable the following
option when running bricks with the global thread pool:

   performance.iot-pass-through = on

To enable it for a FUSE mount point, the option '--global-threading'
must be added to the mount command. To change it, an umount and remount
is needed. It's recommended to disable the following option when using
global threading on a mount point:

   performance.client-io-threads = off

To enable it for services managed by glusterd, glusterd needs to be
started with option '--global-threading'. In this case all daemons, like
self-heal, will be using the global thread pool.

Currently it can only be enabled for bricks, FUSE mounts and glusterd
services.

The maximum number of threads for clients and bricks can be configured
using the following options:

   config.client-threads
   config.brick-threads

These options can be applied online and its effect is immediate most of
the times. If one of them is set to 0, the maximum number of threads
will be calcutated as #cores * 2.

Some distributions use a very old userspace-rcu library (version 0.7)
for this reason, some header files from version 0.10 have been copied
into contrib/userspace-rcu and are used if the detected version is 0.7
or older.

An additional change has been made to io-threads to prevent that threads
are started when iot-pass-through is set.

Change-Id: I09d19e246b9e6d53c6247b29dfca6af6ee00a24b
updates: #532
Signed-off-by: Xavi Hernandez <xhernandez@redhat.com>

1 files changed, 216 insertions, 0 deletions

diff --git a/contrib/userspace-rcu/wfcqueue.h b/contrib/userspace-rcu/wfcqueue.h
new file mode 100644
index 00000000000..0292585ac79
--- /dev/null
+++ b/contrib/userspace-rcu/wfcqueue.h
@@ -0,0 +1,216 @@
+#ifndef _URCU_WFCQUEUE_H
+#define _URCU_WFCQUEUE_H
+
+/*
+ * urcu/wfcqueue.h
+ *
+ * Userspace RCU library - Concurrent Queue with Wait-Free Enqueue/Blocking Dequeue
+ *
+ * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright 2011-2012 - Lai Jiangshan <laijs@cn.fujitsu.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/* Adapted from userspace-rcu 0.10 because version 0.7 doesn't contain it.
+ * The non-LGPL section has been removed. */
+
+#include <pthread.h>
+#include <assert.h>
+#include <stdbool.h>
+#include <urcu/compiler.h>
+#include <urcu/arch.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Concurrent queue with wait-free enqueue/blocking dequeue.
+ *
+ * This queue has been designed and implemented collaboratively by
+ * Mathieu Desnoyers and Lai Jiangshan. Inspired from
+ * half-wait-free/half-blocking queue implementation done by Paul E.
+ * McKenney.
+ */
+
+#define CDS_WFCQ_WOULDBLOCK	((struct cds_wfcq_node *) -1UL)
+
+enum cds_wfcq_ret {
+	CDS_WFCQ_RET_WOULDBLOCK =	-1,
+	CDS_WFCQ_RET_DEST_EMPTY =	0,
+	CDS_WFCQ_RET_DEST_NON_EMPTY =	1,
+	CDS_WFCQ_RET_SRC_EMPTY = 	2,
+};
+
+enum cds_wfcq_state {
+	CDS_WFCQ_STATE_LAST =		(1U << 0),
+};
+
+struct cds_wfcq_node {
+	struct cds_wfcq_node *next;
+};
+
+/*
+ * Do not put head and tail on the same cache-line if concurrent
+ * enqueue/dequeue are expected from many CPUs. This eliminates
+ * false-sharing between enqueue and dequeue.
+ */
+struct __cds_wfcq_head {
+	struct cds_wfcq_node node;
+};
+
+struct cds_wfcq_head {
+	struct cds_wfcq_node node;
+	pthread_mutex_t lock;
+};
+
+#ifndef __cplusplus
+/*
+ * The transparent union allows calling functions that work on both
+ * struct cds_wfcq_head and struct __cds_wfcq_head on any of those two
+ * types.
+ */
+typedef union {
+	struct __cds_wfcq_head *_h;
+	struct cds_wfcq_head *h;
+} __attribute__((__transparent_union__)) cds_wfcq_head_ptr_t;
+
+/*
+ * This static inline is only present for compatibility with C++. It is
+ * effect-less in C.
+ */
+static inline struct __cds_wfcq_head *__cds_wfcq_head_cast(struct __cds_wfcq_head *head)
+{
+	return head;
+}
+
+/*
+ * This static inline is only present for compatibility with C++. It is
+ * effect-less in C.
+ */
+static inline struct cds_wfcq_head *cds_wfcq_head_cast(struct cds_wfcq_head *head)
+{
+	return head;
+}
+#else /* #ifndef __cplusplus */
+
+/* C++ ignores transparent union. */
+typedef union {
+	struct __cds_wfcq_head *_h;
+	struct cds_wfcq_head *h;
+} cds_wfcq_head_ptr_t;
+
+/* C++ ignores transparent union. Requires an explicit conversion. */
+static inline cds_wfcq_head_ptr_t __cds_wfcq_head_cast(struct __cds_wfcq_head *head)
+{
+	cds_wfcq_head_ptr_t ret = { ._h = head };
+	return ret;
+}
+/* C++ ignores transparent union. Requires an explicit conversion. */
+static inline cds_wfcq_head_ptr_t cds_wfcq_head_cast(struct cds_wfcq_head *head)
+{
+	cds_wfcq_head_ptr_t ret = { .h = head };
+	return ret;
+}
+#endif /* #else #ifndef __cplusplus */
+
+struct cds_wfcq_tail {
+	struct cds_wfcq_node *p;
+};
+
+#include "static-wfcqueue.h"
+
+#define cds_wfcq_node_init		_cds_wfcq_node_init
+#define cds_wfcq_init			_cds_wfcq_init
+#define __cds_wfcq_init			___cds_wfcq_init
+#define cds_wfcq_destroy		_cds_wfcq_destroy
+#define cds_wfcq_empty			_cds_wfcq_empty
+#define cds_wfcq_enqueue		_cds_wfcq_enqueue
+
+/* Dequeue locking */
+#define cds_wfcq_dequeue_lock		_cds_wfcq_dequeue_lock
+#define cds_wfcq_dequeue_unlock		_cds_wfcq_dequeue_unlock
+
+/* Locking performed within cds_wfcq calls. */
+#define cds_wfcq_dequeue_blocking	_cds_wfcq_dequeue_blocking
+#define cds_wfcq_dequeue_with_state_blocking	\
+					_cds_wfcq_dequeue_with_state_blocking
+#define cds_wfcq_splice_blocking	_cds_wfcq_splice_blocking
+#define cds_wfcq_first_blocking		_cds_wfcq_first_blocking
+#define cds_wfcq_next_blocking		_cds_wfcq_next_blocking
+
+/* Locking ensured by caller by holding cds_wfcq_dequeue_lock() */
+#define __cds_wfcq_dequeue_blocking	___cds_wfcq_dequeue_blocking
+#define __cds_wfcq_dequeue_with_state_blocking	\
+					___cds_wfcq_dequeue_with_state_blocking
+#define __cds_wfcq_splice_blocking	___cds_wfcq_splice_blocking
+#define __cds_wfcq_first_blocking	___cds_wfcq_first_blocking
+#define __cds_wfcq_next_blocking	___cds_wfcq_next_blocking
+
+/*
+ * Locking ensured by caller by holding cds_wfcq_dequeue_lock().
+ * Non-blocking: deque, first, next return CDS_WFCQ_WOULDBLOCK if they
+ * need to block. splice returns nonzero if it needs to block.
+ */
+#define __cds_wfcq_dequeue_nonblocking	___cds_wfcq_dequeue_nonblocking
+#define __cds_wfcq_dequeue_with_state_nonblocking	\
+				___cds_wfcq_dequeue_with_state_nonblocking
+#define __cds_wfcq_splice_nonblocking	___cds_wfcq_splice_nonblocking
+#define __cds_wfcq_first_nonblocking	___cds_wfcq_first_nonblocking
+#define __cds_wfcq_next_nonblocking	___cds_wfcq_next_nonblocking
+
+/*
+ * __cds_wfcq_for_each_blocking: Iterate over all nodes in a queue,
+ * without dequeuing them.
+ * @head: head of the queue (struct cds_wfcq_head or __cds_wfcq_head pointer).
+ * @tail: tail of the queue (struct cds_wfcq_tail pointer).
+ * @node: iterator on the queue (struct cds_wfcq_node pointer).
+ *
+ * Content written into each node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
+ */
+#define __cds_wfcq_for_each_blocking(head, tail, node)		\
+	for (node = __cds_wfcq_first_blocking(head, tail);	\
+		node != NULL;					\
+		node = __cds_wfcq_next_blocking(head, tail, node))
+
+/*
+ * __cds_wfcq_for_each_blocking_safe: Iterate over all nodes in a queue,
+ * without dequeuing them. Safe against deletion.
+ * @head: head of the queue (struct cds_wfcq_head or __cds_wfcq_head pointer).
+ * @tail: tail of the queue (struct cds_wfcq_tail pointer).
+ * @node: iterator on the queue (struct cds_wfcq_node pointer).
+ * @n: struct cds_wfcq_node pointer holding the next pointer (used
+ *     internally).
+ *
+ * Content written into each node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ * Dequeue/splice/iteration mutual exclusion should be ensured by the
+ * caller.
+ */
+#define __cds_wfcq_for_each_blocking_safe(head, tail, node, n)		       \
+	for (node = __cds_wfcq_first_blocking(head, tail),		       \
+			n = (node ? __cds_wfcq_next_blocking(head, tail, node) : NULL); \
+		node != NULL;						       \
+		node = n, n = (node ? __cds_wfcq_next_blocking(head, tail, node) : NULL))
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_WFCQUEUE_H */