rcu: Add documentation for the new rcuexp debugfs trace file
This commit adds the documentation of the rcuexp debugfs trace file
that records statistics for expedited grace periods.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 79ce989..c776968 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -41,6 +41,8 @@
rcudata:
Displays fields in struct rcu_data.
+rcuexp:
+ Displays statistics for expedited grace periods.
rcugp:
Displays grace-period counters.
rcuhier:
@@ -233,6 +235,45 @@
This field is displayed only for CONFIG_RCU_BOOST kernels.
+The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
+
+s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
+
+These fields are as follows:
+
+o "s" is the starting sequence number.
+
+o "d" is the ending sequence number. When the starting and ending
+ numbers differ, there is an expedited grace period in progress.
+
+o "w" is the number of times that the sequence numbers have been
+ in danger of wrapping.
+
+o "tf" is the number of times that contention has resulted in a
+ failure to begin an expedited grace period.
+
+o "wd1" and "wd2" are the number of times that an attempt to
+ start an expedited grace period found that someone else had
+ completed an expedited grace period that satisfies the
+ attempted request. "Our work is done."
+
+o "n" is number of times that contention was so great that
+ the request was demoted from an expedited grace period to
+ a normal grace period.
+
+o "sc" is the number of times that the attempt to start a
+ new expedited grace period succeeded.
+
+o "dt" is the number of times that we attempted to update
+ the "d" counter.
+
+o "dl" is the number of times that we failed to update the "d"
+ counter.
+
+o "dx" is the number of times that we succeeded in updating
+ the "d" counter.
+
+
The output of "cat rcu/rcu_preempt/rcugp" looks as follows:
completed=31249 gpnum=31250 age=1 max=18