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| author | Paul E. McKenney <paulmck@us.ibm.com> | 2006-10-04 02:17:02 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-10-04 07:55:30 -0700 |
| commit | 621934ee7ed5b073c7fd638b347e632c53572761 (patch) | |
| tree | 5722f9cda22c099ad60545f963410dcbc762ee65 /Documentation/RCU/rcu.txt | |
| parent | 95d77884c77beed676036d2f74d10b470a483c63 (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/rcu.txt')
| -rw-r--r-- | Documentation/RCU/rcu.txt | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt index 02e27bf1d365..f84407cba816 100644 --- a/Documentation/RCU/rcu.txt +++ b/Documentation/RCU/rcu.txt @@ -45,7 +45,8 @@ o How can I see where RCU is currently used in the Linux kernel? Search for "rcu_read_lock", "rcu_read_unlock", "call_rcu", "rcu_read_lock_bh", "rcu_read_unlock_bh", "call_rcu_bh", - "synchronize_rcu", and "synchronize_net". + "srcu_read_lock", "srcu_read_unlock", "synchronize_rcu", + "synchronize_net", and "synchronize_srcu". o What guidelines should I follow when writing code that uses RCU? |