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author | Paul E. McKenney <paulmck@us.ibm.com> | 2006-10-04 09:17:02 (GMT) |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-10-04 14:55:30 (GMT) |
commit | 621934ee7ed5b073c7fd638b347e632c53572761 (patch) | |
tree | 5722f9cda22c099ad60545f963410dcbc762ee65 /Documentation/RCU/whatisRCU.txt | |
parent | 95d77884c77beed676036d2f74d10b470a483c63 (diff) | |
download | linux-fsl-qoriq-621934ee7ed5b073c7fd638b347e632c53572761.tar.xz |
[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')
-rw-r--r-- | Documentation/RCU/whatisRCU.txt | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 820fee2..e0d6d99 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -778,6 +778,8 @@ Markers for RCU read-side critical sections: rcu_read_unlock rcu_read_lock_bh rcu_read_unlock_bh + srcu_read_lock + srcu_read_unlock RCU pointer/list traversal: @@ -804,6 +806,7 @@ RCU grace period: synchronize_net synchronize_sched synchronize_rcu + synchronize_srcu call_rcu call_rcu_bh |