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authorOleg Nesterov <oleg@redhat.com>2015-08-21 19:42:44 +0200
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-10-06 11:25:04 -0700
commitcc44ca848f5e517aeca9f5eabbe13609a3f71450 (patch)
tree4380962c131d6585f347aee962b0280176ae4bdd /include/linux/rcu_sync.h
parent3836f5337f74fedc15981688c3c31dbf4293ae84 (diff)
rcu: Create rcu_sync infrastructure
The rcu_sync infrastructure can be thought of as infrastructure to be used to implement reader-writer primitives having extremely lightweight readers during times when there are no writers. The first use is in the percpu_rwsem used by the VFS subsystem. This infrastructure is functionally equivalent to struct rcu_sync_struct { atomic_t counter; }; /* Check possibility of fast-path read-side operations. */ static inline bool rcu_sync_is_idle(struct rcu_sync_struct *rss) { return atomic_read(&rss->counter) == 0; } /* Tell readers to use slowpaths. */ static inline void rcu_sync_enter(struct rcu_sync_struct *rss) { atomic_inc(&rss->counter); synchronize_sched(); } /* Allow readers to once again use fastpaths. */ static inline void rcu_sync_exit(struct rcu_sync_struct *rss) { synchronize_sched(); atomic_dec(&rss->counter); } The main difference is that it records the state and only calls synchronize_sched() if required. At least some of the calls to synchronize_sched() will be optimized away when rcu_sync_enter() and rcu_sync_exit() are invoked repeatedly in quick succession. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'include/linux/rcu_sync.h')
-rw-r--r--include/linux/rcu_sync.h94
1 files changed, 94 insertions, 0 deletions
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
new file mode 100644
index 000000000000..cb044df2e21c
--- /dev/null
+++ b/include/linux/rcu_sync.h
@@ -0,0 +1,94 @@
+/*
+ * RCU-based infrastructure for lightweight reader-writer locking
+ *
+ * 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 program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (c) 2015, Red Hat, Inc.
+ *
+ * Author: Oleg Nesterov <oleg@redhat.com>
+ */
+
+#ifndef _LINUX_RCU_SYNC_H_
+#define _LINUX_RCU_SYNC_H_
+
+#include <linux/wait.h>
+#include <linux/rcupdate.h>
+
+/* Structure to mediate between updaters and fastpath-using readers. */
+struct rcu_sync {
+ int gp_state;
+ int gp_count;
+ wait_queue_head_t gp_wait;
+
+ int cb_state;
+ struct rcu_head cb_head;
+
+ void (*sync)(void);
+ void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
+};
+
+#define ___RCU_SYNC_INIT(name) \
+ .gp_state = 0, \
+ .gp_count = 0, \
+ .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
+ .cb_state = 0
+
+#define __RCU_SCHED_SYNC_INIT(name) { \
+ ___RCU_SYNC_INIT(name), \
+ .sync = synchronize_sched, \
+ .call = call_rcu_sched, \
+}
+
+#define __RCU_BH_SYNC_INIT(name) { \
+ ___RCU_SYNC_INIT(name), \
+ .sync = synchronize_rcu_bh, \
+ .call = call_rcu_bh, \
+}
+
+#define __RCU_SYNC_INIT(name) { \
+ ___RCU_SYNC_INIT(name), \
+ .sync = synchronize_rcu, \
+ .call = call_rcu, \
+}
+
+#define DEFINE_RCU_SCHED_SYNC(name) \
+ struct rcu_sync name = __RCU_SCHED_SYNC_INIT(name)
+
+#define DEFINE_RCU_BH_SYNC(name) \
+ struct rcu_sync name = __RCU_BH_SYNC_INIT(name)
+
+#define DEFINE_RCU_SYNC(name) \
+ struct rcu_sync name = __RCU_SYNC_INIT(name)
+
+/**
+ * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * Returns true if readers are permitted to use their fastpaths.
+ * Must be invoked within an RCU read-side critical section whose
+ * flavor matches that of the rcu_sync struture.
+ */
+static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
+{
+ return !rsp->gp_state; /* GP_IDLE */
+}
+
+enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
+
+extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_enter(struct rcu_sync *);
+extern void rcu_sync_exit(struct rcu_sync *);
+
+#endif /* _LINUX_RCU_SYNC_H_ */