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author | Paul E. McKenney <paulmck@us.ibm.com> | 2006-10-04 02:17:02 -0700 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-10-04 07:55:30 -0700 |
commit | 621934ee7ed5b073c7fd638b347e632c53572761 (patch) | |
tree | 5722f9cda22c099ad60545f963410dcbc762ee65 /include | |
parent | 95d77884c77beed676036d2f74d10b470a483c63 (diff) | |
download | linux-621934ee7ed5b073c7fd638b347e632c53572761.tar.bz2 |
[PATCH] srcu-3: RCU variant permitting read-side blocking
Updated patch adding a variant of RCU that permits sleeping in read-side
critical sections. SRCU is as follows:
o Each use of SRCU creates its own srcu_struct, and each
srcu_struct has its own set of grace periods. This is
critical, as it prevents one subsystem with a blocking
reader from holding up SRCU grace periods for other
subsystems.
o The SRCU primitives (srcu_read_lock(), srcu_read_unlock(),
and synchronize_srcu()) all take a pointer to a srcu_struct.
o The SRCU primitives must be called from process context.
o srcu_read_lock() returns an int that must be passed to
the matching srcu_read_unlock(). Realtime RCU avoids the
need for this by storing the state in the task struct,
but SRCU needs to allow a given code path to pass through
multiple SRCU domains -- storing state in the task struct
would therefore require either arbitrary space in the
task struct or arbitrary limits on SRCU nesting. So I
kicked the state-storage problem up to the caller.
Of course, it is not permitted to call synchronize_srcu()
while in an SRCU read-side critical section.
o There is no call_srcu(). It would not be hard to implement
one, but it seems like too easy a way to OOM the system.
(Hey, we have enough trouble with call_rcu(), which does
-not- permit readers to sleep!!!) So, if you want it,
please tell me why...
[josht@us.ibm.com: sparse notation]
Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Josh Triplett <josh@freedesktop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/srcu.h | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/include/linux/srcu.h b/include/linux/srcu.h new file mode 100644 index 000000000000..947fdab2ddb0 --- /dev/null +++ b/include/linux/srcu.h @@ -0,0 +1,49 @@ +/* + * Sleepable Read-Copy Update mechanism for mutual exclusion + * + * 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, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * + * Copyright (C) IBM Corporation, 2006 + * + * Author: Paul McKenney <paulmck@us.ibm.com> + * + * For detailed explanation of Read-Copy Update mechanism see - + * Documentation/RCU/ *.txt + * + */ + +struct srcu_struct_array { + int c[2]; +}; + +struct srcu_struct { + int completed; + struct srcu_struct_array *per_cpu_ref; + struct mutex mutex; +}; + +#ifndef CONFIG_PREEMPT +#define srcu_barrier() barrier() +#else /* #ifndef CONFIG_PREEMPT */ +#define srcu_barrier() +#endif /* #else #ifndef CONFIG_PREEMPT */ + +void init_srcu_struct(struct srcu_struct *sp); +void cleanup_srcu_struct(struct srcu_struct *sp); +int srcu_read_lock(struct srcu_struct *sp) __acquires(sp); +void srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp); +void synchronize_srcu(struct srcu_struct *sp); +long srcu_batches_completed(struct srcu_struct *sp); +void cleanup_srcu_struct(struct srcu_struct *sp); |