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Commit 90e6ac36 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: update tracing documentation for new rcutorture and rcuboost 



This commit documents the new debugfs rcu/rcutorture and rcu/rcuboost
trace files.  The description has been updated as suggested by Josh
Triplett.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 4a298656

Documentation/RCU/trace.txt

+161 −25
Original line number Diff line number Diff line
@@ -10,34 +10,46 @@ for rcutree and next for rcutiny. 


CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats



These implementations of RCU provides five debugfs files under the

top-level directory RCU: rcu/rcudata (which displays fields in struct

rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of

rcu/rcudata), rcu/rcugp (which displays grace-period counters),

rcu/rcuhier (which displays the struct rcu_node hierarchy), and

rcu/rcu_pending (which displays counts of the reasons that the

rcu_pending() function decided that there was core RCU work to do).

These implementations of RCU provides several debugfs files under the

top-level directory "rcu":



rcu/rcudata:

	Displays fields in struct rcu_data.

rcu/rcudata.csv:

	Comma-separated values spreadsheet version of rcudata.

rcu/rcugp:

	Displays grace-period counters.

rcu/rcuhier:

	Displays the struct rcu_node hierarchy.

rcu/rcu_pending:

	Displays counts of the reasons rcu_pending() decided that RCU had

	work to do.

rcu/rcutorture:

	Displays rcutorture test progress.

rcu/rcuboost:

	Displays RCU boosting statistics.  Only present if

	CONFIG_RCU_BOOST=y.



The output of "cat rcu/rcudata" looks as follows:



rcu_sched:

  0!c=423090 g=423091 pq=1 pqc=423090 qp=1 dt=86475/1/0 df=16319 of=163 ri=1519 ql=0 qs=.... b=10 ci=1460693 co=1648 ca=6448

  1!c=423329 g=423330 pq=1 pqc=423329 qp=1 dt=90875/1/0 df=16231 of=157 ri=1249 ql=0 qs=.... b=10 ci=1459002 co=1614 ca=3310

  2!c=423370 g=423371 pq=1 pqc=423370 qp=1 dt=69661/1/0 df=16125 of=163 ri=1469 ql=0 qs=.... b=10 ci=1610701 co=2015 ca=2378

  3!c=422967 g=422968 pq=1 pqc=422967 qp=1 dt=70349/1/0 df=12528 of=163 ri=1450 ql=0 qs=.... b=10 ci=1427543 co=1430 ca=897

  4!c=423196 g=423197 pq=1 pqc=423196 qp=0 dt=38935/1/0 df=10959 of=177 ri=1657 ql=0 qs=.... b=10 ci=1562249 co=1896 ca=533

  5!c=422950 g=422951 pq=1 pqc=422950 qp=0 dt=25127/1/0 df=5895 of=167 ri=1549 ql=0 qs=.... b=10 ci=1777260 co=2137 ca=274

  6!c=423396 g=423397 pq=1 pqc=423396 qp=1 dt=22639/1/0 df=4590 of=149 ri=1572 ql=0 qs=.... b=10 ci=1471186 co=1530 ca=243

  7 c=460203 g=460203 pq=1 pqc=460202 qp=0 dt=937087/1/0 df=3298 of=149 ri=1584 ql=6 qs=N.W. b=10 ci=4026154 co=1948 ca=135

  0!c=423090 g=423091 pq=1 pqc=423090 qp=1 dt=86475/1/0 df=16319 of=163 ri=1519 ql=0 qs=.... kt=0/W b=10 ci=1460693 co=1648 ca=6448

  1!c=423329 g=423330 pq=1 pqc=423329 qp=1 dt=90875/1/0 df=16231 of=157 ri=1249 ql=0 qs=.... kt=0/W b=10 ci=1459002 co=1614 ca=3310

  2!c=423370 g=423371 pq=1 pqc=423370 qp=1 dt=69661/1/0 df=16125 of=163 ri=1469 ql=0 qs=.... kt=0/W b=10 ci=1610701 co=2015 ca=2378

  3!c=422967 g=422968 pq=1 pqc=422967 qp=1 dt=70349/1/0 df=12528 of=163 ri=1450 ql=0 qs=.... kt=0/W b=10 ci=1427543 co=1430 ca=897

  4!c=423196 g=423197 pq=1 pqc=423196 qp=0 dt=38935/1/0 df=10959 of=177 ri=1657 ql=0 qs=.... kt=0/W b=10 ci=1562249 co=1896 ca=533

  5!c=422950 g=422951 pq=1 pqc=422950 qp=0 dt=25127/1/0 df=5895 of=167 ri=1549 ql=0 qs=.... kt=0/W b=10 ci=1777260 co=2137 ca=274

  6!c=423396 g=423397 pq=1 pqc=423396 qp=1 dt=22639/1/0 df=4590 of=149 ri=1572 ql=0 qs=.... kt=0/W b=10 ci=1471186 co=1530 ca=243

  7 c=460203 g=460203 pq=1 pqc=460202 qp=0 dt=937087/1/0 df=3298 of=149 ri=1584 ql=6 qs=N.W. kt=0/W b=10 ci=4026154 co=1948 ca=135

rcu_bh:

  0!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=86475/1/0 df=11 of=0 ri=0 ql=0 qs=.... b=10 ci=112 co=0 ca=0

  1!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=90875/1/0 df=15 of=0 ri=0 ql=0 qs=.... b=10 ci=143 co=0 ca=0

  2!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=69661/1/0 df=21 of=0 ri=1 ql=0 qs=.... b=10 ci=88 co=0 ca=0

  3!c=18446744073709551494 g=18446744073709551494 pq=1 pqc=18446744073709551493 qp=0 dt=70349/1/0 df=13 of=0 ri=0 ql=0 qs=....  b=10 ci=100 co=0 ca=0

  4!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=38935/1/0 df=17 of=0 ri=0 ql=0 qs=....  b=10 ci=36 co=0 ca=0

  5!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=25127/1/0 df=7 of=0 ri=0 ql=0 qs=....  b=10 ci=32 co=0 ca=0

  6!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=22639/1/0 df=9 of=0 ri=0 ql=0 qs=....  b=10 ci=44 co=0 ca=0

  7 c=182 g=182 pq=1 pqc=181 qp=0 dt=937087/1/0 df=14 of=0 ri=1 ql=0 qs=....  b=10 ci=627 co=0 ca=0

  0!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=86475/1/0 df=11 of=0 ri=0 ql=0 qs=.... kt=0/W b=10 ci=112 co=0 ca=0

  1!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=90875/1/0 df=15 of=0 ri=0 ql=0 qs=.... kt=0/W b=10 ci=143 co=0 ca=0

  2!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=69661/1/0 df=21 of=0 ri=1 ql=0 qs=.... kt=0/W b=10 ci=88 co=0 ca=0

  3!c=18446744073709551494 g=18446744073709551494 pq=1 pqc=18446744073709551493 qp=0 dt=70349/1/0 df=13 of=0 ri=0 ql=0 qs=....  kt=0/W b=10 ci=100 co=0 ca=0

  4!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=38935/1/0 df=17 of=0 ri=0 ql=0 qs=....  kt=0/W b=10 ci=36 co=0 ca=0

  5!c=18446744073709551494 g=18446744073709551494 pq=0 pqc=18446744073709551493 qp=1 dt=25127/1/0 df=7 of=0 ri=0 ql=0 qs=....  kt=0/W b=10 ci=32 co=0 ca=0

  6!c=18446744073709551496 g=18446744073709551496 pq=1 pqc=18446744073709551495 qp=0 dt=22639/1/0 df=9 of=0 ri=0 ql=0 qs=....  kt=0/W b=10 ci=44 co=0 ca=0

  7 c=182 g=182 pq=1 pqc=181 qp=0 dt=937087/1/0 df=14 of=0 ri=1 ql=0 qs=....  kt=0/W b=10 ci=627 co=0 ca=0



The first section lists the rcu_data structures for rcu_sched, the second

for rcu_bh.  Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
@@ -146,6 +158,23 @@ o "qs" gives an indication of the state of the callback queue 
	If there are no callbacks in a given one of the above states,

	the corresponding character is replaced by ".".



o	"kt" is the per-CPU kernel-thread state.  The digit preceding

	the slash is zero if there is no work pending and 1 otherwise.

	The character after the slash is as follows:



	"S"	The kernel thread is stopped, in other words, all

		CPUs corresponding to this rcu_node structure are

		offline.



	"R"	The kernel thread is running.



	"W"	The kernel thread is waiting because there is no work

		for it to do.



	"Y"	The kernel thread is yielding to avoid hogging CPU.



	"?"	Unknown value, indicates a bug.



o	"b" is the batch limit for this CPU.  If more than this number

	of RCU callbacks is ready to invoke, then the remainder will

	be deferred.
@@ -356,6 +385,113 @@ o "nn" is the number of times that this CPU needed nothing. Alert 
	is due to short-circuit evaluation in rcu_pending().





The output of "cat rcu/rcutorture" looks as follows:



rcutorture test sequence: 0 (test in progress)

rcutorture update version number: 615



The first line shows the number of rcutorture tests that have completed

since boot.  If a test is currently running, the "(test in progress)"

string will appear as shown above.  The second line shows the number of

update cycles that the current test has started, or zero if there is

no test in progress.





The output of "cat rcu/rcuboost" looks as follows:



0:5 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f

     balk: nt=0 egt=989 bt=0 nb=0 ny=0 nos=16

6:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f

     balk: nt=0 egt=225 bt=0 nb=0 ny=0 nos=6



This information is output only for rcu_preempt.  Each two-line entry

corresponds to a leaf rcu_node strcuture.  The fields are as follows:



o	"n:m" is the CPU-number range for the corresponding two-line

	entry.  In the sample output above, the first entry covers

	CPUs zero through five and the second entry covers CPUs 6

	and 7.



o	"tasks=TNEB" gives the state of the various segments of the

	rnp->blocked_tasks list:



	"T"	This indicates that there are some tasks that blocked

		while running on one of the corresponding CPUs while

		in an RCU read-side critical section.



	"N"	This indicates that some of the blocked tasks are preventing

		the current normal (non-expedited) grace period from

		completing.



	"E"	This indicates that some of the blocked tasks are preventing

		the current expedited grace period from completing.



	"B"	This indicates that some of the blocked tasks are in

		need of RCU priority boosting.



	Each character is replaced with "." if the corresponding

	condition does not hold.



o	"kt" is the state of the RCU priority-boosting kernel

	thread associated with the corresponding rcu_node structure.

	The state can be one of the following:



	"S"	The kernel thread is stopped, in other words, all

		CPUs corresponding to this rcu_node structure are

		offline.



	"R"	The kernel thread is running.



	"W"	The kernel thread is waiting because there is no work

		for it to do.



	"Y"	The kernel thread is yielding to avoid hogging CPU.



	"?"	Unknown value, indicates a bug.



o	"ntb" is the number of tasks boosted.



o	"neb" is the number of tasks boosted in order to complete an

	expedited grace period.



o	"nnb" is the number of tasks boosted in order to complete a

	normal (non-expedited) grace period.  When boosting a task

	that was blocking both an expedited and a normal grace period,

	it is counted against the expedited total above.



o	"j" is the low-order 16 bits of the jiffies counter in

	hexadecimal.



o	"bt" is the low-order 16 bits of the value that the jiffies

	counter will have when we next start boosting, assuming that

	the current grace period does not end beforehand.  This is

	also in hexadecimal.



o	"balk: nt" counts the number of times we didn't boost (in

	other words, we balked) even though it was time to boost because

	there were no blocked tasks to boost.  This situation occurs

	when there is one blocked task on one rcu_node structure and

	none on some other rcu_node structure.



o	"egt" counts the number of times we balked because although

	there were blocked tasks, none of them were blocking the

	current grace period, whether expedited or otherwise.



o	"bt" counts the number of times we balked because boosting

	had already been initiated for the current grace period.



o	"nb" counts the number of times we balked because there

	was at least one task blocking the current non-expedited grace

	period that never had blocked.  If it is already running, it

	just won't help to boost its priority!



o	"ny" counts the number of times we balked because it was

	not yet time to start boosting.



o	"nos" counts the number of times we balked for other

	reasons, e.g., the grace period ended first.





CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats



These implementations of RCU provides a single debugfs file under the
@@ -422,9 +558,9 @@ o "neb" is the number of expedited grace periods that have had 
o	"nnb" is the number of normal grace periods that have had

	to resort to RCU priority boosting since boot.



o	"j" is the low-order 12 bits of the jiffies counter in hexadecimal.

o	"j" is the low-order 16 bits of the jiffies counter in hexadecimal.



o	"bt" is the low-order 12 bits of the value that the jiffies counter

o	"bt" is the low-order 16 bits of the value that the jiffies counter

	will have at the next time that boosting is scheduled to begin.



o	In the line beginning with "normal balk", the fields are as follows: