linux-stable.git/include/linux/rcupdate.h, branch linux-2.6.25.y

Remove rcu_assign_pointer() penalty for NULL pointers

2008-02-06T18:41:06+00:00

The rcu_assign_pointer() primitive currently unconditionally executes a
memory barrier, even when a NULL pointer is being assigned.  This has lead
some to avoid using rcu_assign_pointer() for NULL pointers, which loses the
self-documenting advantages of rcu_assign_pointer() This patch uses
__builtin_const_p() to omit needless memory barriers for NULL-pointer
assignments at compile time with no runtime penalty, as discussed in the
following thread:

	http://www.mail-archive.com/netdev@vger.kernel.org/msg54852.html

Tested on x86_64 and ppc64, also compiled the four cases (NULL/non-NULL
and const/non-const) with gcc version 4.1.2, and hand-checked the
assembly output.

Signed-off-by: Paul E. McKenney 
Acked-by: Herbert Xu 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Preempt-RCU: implementation

2008-01-25T20:08:24+00:00

This patch implements a new version of RCU which allows its read-side
critical sections to be preempted. It uses a set of counter pairs
to keep track of the read-side critical sections and flips them
when all tasks exit read-side critical section. The details
of this implementation can be found in this paper -

	http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf

and the article-

	http://lwn.net/Articles/253651/

This patch was developed as a part of the -rt kernel development and
meant to provide better latencies when read-side critical sections of
RCU don't disable preemption.  As a consequence of keeping track of RCU
readers, the readers have a slight overhead (optimizations in the paper).
This implementation co-exists with the "classic" RCU implementations
and can be switched to at compiler.

Also includes RCU tracing summarized in debugfs.

[ akpm@linux-foundation.org: build fixes on non-preempt architectures ]

Signed-off-by: Gautham R Shenoy 
Signed-off-by: Dipankar Sarma 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Steven Rostedt 
Signed-off-by: Ingo Molnar

Preempt-RCU: reorganize RCU code into rcuclassic.c and rcupdate.c

2008-01-25T20:08:24+00:00

This patch re-organizes the RCU code to enable multiple implementations
of RCU. Users of RCU continues to include rcupdate.h and the
RCU interfaces remain the same. This is in preparation for
subsequently merging the preemptible RCU implementation.

Signed-off-by: Gautham R Shenoy 
Signed-off-by: Dipankar Sarma 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Steven Rostedt 
Signed-off-by: Ingo Molnar

Immunize rcu_dereference() against crazy compiler writers

2007-10-17T15:42:46+00:00

Turns out that compiler writers are a bit more aggressive about optimizing
than one might expect.  This patch prevents a number of such optimizations
from messing up rcu_deference().  This is not merely a theoretical problem, as
evidenced by the rmb() in mce_log().

Signed-off-by: Paul E. McKenney 
Cc: Ingo Molnar 
Acked-by: Josh Triplett 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

lockdep: annotate rcu_read_{,un}lock{,_bh}

2007-10-11T20:11:12+00:00

lockdep annotate rcu_read_{,un}lock{,_bh} in order to catch imbalanced
usage.

Signed-off-by: Peter Zijlstra 
Signed-off-by: Ingo Molnar 
Cc: Paul E. McKenney

RCU: Remove prototype for nonexistent function synchronize_idle()

2007-08-11T22:47:41+00:00

synchronize_idle() sounds like an interesting function, but we don't
actually have it, so don't prototype it.  Introduced in commit
9b06e818985d139fd9e82c28297f7744e1b484e1, in 2005.

Signed-off-by: Josh Triplett 
Acked-by: Paul E. McKenney 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] RCU: CREDITS and MAINTAINERS

2006-10-04T14:55:31+00:00

Add MAINTAINERS entry for Read-Copy Update (RCU), listing Dipankar Sarma as
maintainer, and giving the URL for Paul McKenney's RCU site.  Add
MAINTAINERS entry for rcutorture, listing myself as maintainer.  Add
CREDITS entries for developers of RCU, RCU variants, and rcutorture.  Use
Paul McKenney's preferred email address in include/linux/rcupdate.h .

Signed-off-by: Josh Triplett 
Cc: Paul McKenney 
Cc: Dipankar Sarma 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] rcu: simplify/improve batch tuning

2006-10-04T14:55:31+00:00

Kill a hard-to-calculate 'rsinterval' boot parameter and per-cpu
rcu_data.last_rs_qlen.  Instead, it adds adds a flag rcu_ctrlblk.signaled,
which records the fact that one of CPUs has sent a resched IPI since the
last rcu_start_batch().

Roughly speaking, we need two rcu_start_batch()s in order to move callbacks
from ->nxtlist to ->donelist.  This means that when ->qlen exceeds qhimark
and continues to grow, we should send a resched IPI, and then do it again
after we gone through a quiescent state.

On the other hand, if it was already sent, we don't need to do it again
when another CPU detects overflow of the queue.

Signed-off-by: Oleg Nesterov 
Acked-by: Paul E. McKenney 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] rcu: Add lock annotations to RCU locking primitives

2006-06-30T18:25:39+00:00

Add __acquire annotations to rcu_read_lock and rcu_read_lock_bh, and add
__release annotations to rcu_read_unlock and rcu_read_unlock_bh.  This
allows sparse to detect improperly paired calls to these functions.

Signed-off-by: Josh Triplett 
Acked-by: Paul E. McKenney 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] rcutorture: add call_rcu_bh() operations

2006-06-28T00:32:40+00:00

Add operations for the call_rcu_bh() variant of RCU.  Also add an
rcu_batches_completed_bh() function, which is needed by rcutorture.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds