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Commit d484a215 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 40e80c46

Documentation/RCU/trace.txt

+41 −0
Original line number Diff line number Diff line
@@ -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