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, 178 insertions, 0 deletions

diff --git a/contrib/userspace-rcu/wfstack.h b/contrib/userspace-rcu/wfstack.h
new file mode 100644
index 00000000000..738fd1cfd33
--- /dev/null
+++ b/contrib/userspace-rcu/wfstack.h
@@ -0,0 +1,178 @@
+#ifndef _URCU_WFSTACK_H
+#define _URCU_WFSTACK_H
+
+/*
+ * urcu/wfstack.h
+ *
+ * Userspace RCU library - Stack with wait-free push, blocking traversal.
+ *
+ * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.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 support a stack
+ * without mutex. The non-LGPL section has been removed. */
+
+#include <pthread.h>
+#include <assert.h>
+#include <stdbool.h>
+#include <urcu/compiler.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Stack with wait-free push, blocking traversal.
+ *
+ * Stack implementing push, pop, pop_all operations, as well as iterator
+ * on the stack head returned by pop_all.
+ *
+ * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
+ *                       cds_wfs_first.
+ * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
+ *                      iteration on stack head returned by pop_all.
+ *
+ * Synchronization table:
+ *
+ * External synchronization techniques described in the API below is
+ * required between pairs marked with "X". No external synchronization
+ * required between pairs marked with "-".
+ *
+ *                      cds_wfs_push  __cds_wfs_pop  __cds_wfs_pop_all
+ * cds_wfs_push               -              -                  -
+ * __cds_wfs_pop              -              X                  X
+ * __cds_wfs_pop_all          -              X                  -
+ *
+ * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
+ * synchronization.
+ */
+
+#define CDS_WFS_WOULDBLOCK	((void *) -1UL)
+
+enum cds_wfs_state {
+	CDS_WFS_STATE_LAST =		(1U << 0),
+};
+
+/*
+ * struct cds_wfs_node is returned by __cds_wfs_pop, and also used as
+ * iterator on stack. It is not safe to dereference the node next
+ * pointer when returned by __cds_wfs_pop_blocking.
+ */
+struct cds_wfs_node {
+	struct cds_wfs_node *next;
+};
+
+/*
+ * struct cds_wfs_head is returned by __cds_wfs_pop_all, and can be used
+ * to begin iteration on the stack. "node" needs to be the first field of
+ * cds_wfs_head, so the end-of-stack pointer value can be used for both
+ * types.
+ */
+struct cds_wfs_head {
+	struct cds_wfs_node node;
+};
+
+struct __cds_wfs_stack {
+	struct cds_wfs_head *head;
+};
+
+struct cds_wfs_stack {
+	struct cds_wfs_head *head;
+	pthread_mutex_t lock;
+};
+
+/*
+ * The transparent union allows calling functions that work on both
+ * struct cds_wfs_stack and struct __cds_wfs_stack on any of those two
+ * types.
+ */
+typedef union {
+	struct __cds_wfs_stack *_s;
+	struct cds_wfs_stack *s;
+} __attribute__((__transparent_union__)) cds_wfs_stack_ptr_t;
+
+#include "static-wfstack.h"
+
+#define cds_wfs_node_init		_cds_wfs_node_init
+#define cds_wfs_init			_cds_wfs_init
+#define cds_wfs_destroy			_cds_wfs_destroy
+#define __cds_wfs_init			___cds_wfs_init
+#define cds_wfs_empty			_cds_wfs_empty
+#define cds_wfs_push			_cds_wfs_push
+
+/* Locking performed internally */
+#define cds_wfs_pop_blocking		_cds_wfs_pop_blocking
+#define cds_wfs_pop_with_state_blocking	_cds_wfs_pop_with_state_blocking
+#define cds_wfs_pop_all_blocking	_cds_wfs_pop_all_blocking
+
+/*
+ * For iteration on cds_wfs_head returned by __cds_wfs_pop_all or
+ * cds_wfs_pop_all_blocking.
+ */
+#define cds_wfs_first			_cds_wfs_first
+#define cds_wfs_next_blocking		_cds_wfs_next_blocking
+#define cds_wfs_next_nonblocking	_cds_wfs_next_nonblocking
+
+/* Pop locking with internal mutex */
+#define cds_wfs_pop_lock		_cds_wfs_pop_lock
+#define cds_wfs_pop_unlock		_cds_wfs_pop_unlock
+
+/* Synchronization ensured by the caller. See synchronization table. */
+#define __cds_wfs_pop_blocking		___cds_wfs_pop_blocking
+#define __cds_wfs_pop_with_state_blocking	\
+					___cds_wfs_pop_with_state_blocking
+#define __cds_wfs_pop_nonblocking	___cds_wfs_pop_nonblocking
+#define __cds_wfs_pop_with_state_nonblocking	\
+					___cds_wfs_pop_with_state_nonblocking
+#define __cds_wfs_pop_all		___cds_wfs_pop_all
+
+#ifdef __cplusplus
+}
+#endif
+
+/*
+ * cds_wfs_for_each_blocking: Iterate over all nodes returned by
+ * __cds_wfs_pop_all().
+ * @head: head of the queue (struct cds_wfs_head pointer).
+ * @node: iterator (struct cds_wfs_node pointer).
+ *
+ * Content written into each node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ */
+#define cds_wfs_for_each_blocking(head, node)			\
+	for (node = cds_wfs_first(head);			\
+		node != NULL;					\
+		node = cds_wfs_next_blocking(node))
+
+/*
+ * cds_wfs_for_each_blocking_safe: Iterate over all nodes returned by
+ * __cds_wfs_pop_all(). Safe against deletion.
+ * @head: head of the queue (struct cds_wfs_head pointer).
+ * @node: iterator (struct cds_wfs_node pointer).
+ * @n: struct cds_wfs_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.
+ */
+#define cds_wfs_for_each_blocking_safe(head, node, n)			   \
+	for (node = cds_wfs_first(head),				   \
+			n = (node ? cds_wfs_next_blocking(node) : NULL);   \
+		node != NULL;						   \
+		node = n, n = (node ? cds_wfs_next_blocking(node) : NULL))
+
+#endif /* _URCU_WFSTACK_H */