path: root/Documentation/RCU/whatisRCU.txt
diff options
authorPaul E. McKenney <paulmck@us.ibm.com>2006-10-04 02:17:02 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-10-04 07:55:30 -0700
commit621934ee7ed5b073c7fd638b347e632c53572761 (patch)
tree5722f9cda22c099ad60545f963410dcbc762ee65 /Documentation/RCU/whatisRCU.txt
parent95d77884c77beed676036d2f74d10b470a483c63 (diff)
[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 'Documentation/RCU/whatisRCU.txt')
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 820fee236967..e0d6d99b8f9b 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -778,6 +778,8 @@ Markers for RCU read-side critical sections:
+ srcu_read_lock
+ srcu_read_unlock
RCU pointer/list traversal:
@@ -804,6 +806,7 @@ RCU grace period:
+ synchronize_srcu