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authorLinus Torvalds <torvalds@linux-foundation.org>2014-08-05 02:55:08 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-05 02:55:08 +0400
commit5bda4f638f36ef4c4e3b1397b02affc3db94356e (patch)
treed1bde148cde9981c31941382b2076084c7f5796c /Documentation
parenta45c657f28f82b056173d1afc2e7ed1f1f68829f (diff)
parent01c9db827146ce321562a992a5dbc1a49b1a99ce (diff)
downloadlinux-5bda4f638f36ef4c4e3b1397b02affc3db94356e.tar.xz
Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU changes from Ingo Molar: "The main changes: - torture-test updates - callback-offloading changes - maintainership changes - update RCU documentation - miscellaneous fixes" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits) rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing rcu: Fix a sparse warning in rcu_report_unblock_qs_rnp() rcu: Fix a sparse warning in rcu_initiate_boost() rcu: Fix __rcu_reclaim() to use true/false for bool rcu: Remove CONFIG_PROVE_RCU_DELAY rcu: Use __this_cpu_read() instead of per_cpu_ptr() rcu: Don't use NMIs to dump other CPUs' stacks rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs rcu: Simplify priority boosting by putting rt_mutex in rcu_node rcu: Check both root and current rcu_node when setting up future grace period rcu: Allow post-unlock reference for rt_mutex rcu: Loosen __call_rcu()'s rcu_head alignment constraint rcu: Eliminate read-modify-write ACCESS_ONCE() calls rcu: Remove redundant ACCESS_ONCE() from tick_do_timer_cpu rcu: Make rcu node arrays static const char * const signal: Explain local_irq_save() call rcu: Handle obsolete references to TINY_PREEMPT_RCU rcu: Document deadlock-avoidance information for rcu_read_unlock() scripts: Teach get_maintainer.pl about the new "R:" tag rcu: Update rcu torture maintainership filename patterns ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/RCU/RTFP.txt4
-rw-r--r--Documentation/RCU/rcuref.txt9
-rw-r--r--Documentation/kernel-parameters.txt7
-rw-r--r--Documentation/memory-barriers.txt27
4 files changed, 41 insertions, 6 deletions
diff --git a/Documentation/RCU/RTFP.txt b/Documentation/RCU/RTFP.txt
index 2f0fcb2112d2..f29bcbc463e7 100644
--- a/Documentation/RCU/RTFP.txt
+++ b/Documentation/RCU/RTFP.txt
@@ -2451,8 +2451,8 @@ lot of {Linux} into your technology!!!"
,month="February"
,year="2010"
,note="Available:
-\url{http://kerneltrap.com/mailarchive/linux-netdev/2010/2/26/6270589}
-[Viewed March 20, 2011]"
+\url{http://thread.gmane.org/gmane.linux.network/153338}
+[Viewed June 9, 2014]"
,annotation={
Use a pair of list_head structures to support RCU-protected
resizable hash tables.
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 141d531aa14b..613033ff2b9b 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -1,5 +1,14 @@
Reference-count design for elements of lists/arrays protected by RCU.
+
+Please note that the percpu-ref feature is likely your first
+stop if you need to combine reference counts and RCU. Please see
+include/linux/percpu-refcount.h for more information. However, in
+those unusual cases where percpu-ref would consume too much memory,
+please read on.
+
+------------------------------------------------------------------------
+
Reference counting on elements of lists which are protected by traditional
reader/writer spinlocks or semaphores are straightforward:
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 45fbea7c329b..90f6139608ff 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2813,6 +2813,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
quiescent states. Units are jiffies, minimum
value is one, and maximum value is HZ.
+ rcutree.rcu_nocb_leader_stride= [KNL]
+ Set the number of NOCB kthread groups, which
+ defaults to the square root of the number of
+ CPUs. Larger numbers reduces the wakeup overhead
+ on the per-CPU grace-period kthreads, but increases
+ that same overhead on each group's leader.
+
rcutree.qhimark= [KNL]
Set threshold of queued RCU callbacks beyond which
batch limiting is disabled.
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index f1dc4a215593..a4de88fb55f0 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -757,10 +757,14 @@ SMP BARRIER PAIRING
When dealing with CPU-CPU interactions, certain types of memory barrier should
always be paired. A lack of appropriate pairing is almost certainly an error.
-A write barrier should always be paired with a data dependency barrier or read
-barrier, though a general barrier would also be viable. Similarly a read
-barrier or a data dependency barrier should always be paired with at least an
-write barrier, though, again, a general barrier is viable:
+General barriers pair with each other, though they also pair with
+most other types of barriers, albeit without transitivity. An acquire
+barrier pairs with a release barrier, but both may also pair with other
+barriers, including of course general barriers. A write barrier pairs
+with a data dependency barrier, an acquire barrier, a release barrier,
+a read barrier, or a general barrier. Similarly a read barrier or a
+data dependency barrier pairs with a write barrier, an acquire barrier,
+a release barrier, or a general barrier:
CPU 1 CPU 2
=============== ===============
@@ -1893,6 +1897,21 @@ between the STORE to indicate the event and the STORE to set TASK_RUNNING:
<general barrier> STORE current->state
LOAD event_indicated
+To repeat, this write memory barrier is present if and only if something
+is actually awakened. To see this, consider the following sequence of
+events, where X and Y are both initially zero:
+
+ CPU 1 CPU 2
+ =============================== ===============================
+ X = 1; STORE event_indicated
+ smp_mb(); wake_up();
+ Y = 1; wait_event(wq, Y == 1);
+ wake_up(); load from Y sees 1, no memory barrier
+ load from X might see 0
+
+In contrast, if a wakeup does occur, CPU 2's load from X would be guaranteed
+to see 1.
+
The available waker functions include:
complete();