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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>
This commit is contained in:
Paul E. McKenney 2012-10-31 13:22:08 -07:00 committed by Paul E. McKenney
parent 40e80c469f
commit d484a21513
1 changed files with 41 additions and 0 deletions
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Documentation/RCU/trace.txt
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@ -41,6 +41,8 @@ also rcu/rcu_preempt) the following files will be present:
rcudata:
Displays fields in struct rcu_data.
rcuexp:
Displays statistics for expedited grace periods.
rcugp:
Displays grace-period counters.
rcuhier:
@ -233,6 +235,45 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of
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