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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-27 13:16:15 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-06-08 08:25:33 -0700
commit09f501a0f0b5ad81f79049a31fb71f99f282d663 (patch)
tree385263714a74806f97706e8b37cdad190f4f1eb9 /Documentation/RCU
parent5d9853f3cf26109ab7b6b7bf414ffe3c739177d4 (diff)
downloadlinux-09f501a0f0b5ad81f79049a31fb71f99f282d663.tar.bz2
srcu: Document auto-expediting requirement
This commit documents the auto-expediting requirement satisfied by commits 2da4b2a7fd8d ("srcu: Expedite first synchronize_srcu() when idle") and 22607d66bbc3 ("srcu: Specify auto-expedite holdoff time"). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/Design/Requirements/Requirements.html14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index f60adf112663..8bbf0bb18389 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2936,6 +2936,20 @@ to whether or not a CPU is online, which means that <tt>srcu_barrier()</tt>
need not exclude CPU-hotplug operations.
<p>
+SRCU also differs from other RCU flavors in that SRCU's expedited and
+non-expedited grace periods are implemented by the same mechanism.
+This means that in the current SRCU implementation, expediting a
+future grace period has the side effect of expediting all prior
+grace periods that have not yet completed.
+(But please note that this is a property of the current implementation,
+not necessarily of future implementations.)
+In addition, if SRCU has been idle for longer than the interval
+specified by the <tt>srcutree.exp_holdoff</tt> kernel boot parameter
+(25&nbsp;microseconds by default),
+and if a <tt>synchronize_srcu()</tt> invocation ends this idle period,
+that invocation will be automatically expedited.
+
+<p>
As of v4.12, SRCU's callbacks are maintained per-CPU, eliminating
a locking bottleneck present in prior kernel versions.
Although this will allow users to put much heavier stress on