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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.

1	CONFIG_RCU_TRACE debugfs Files and Formats
2	
3	
4	The rcutree and rcutiny implementations of RCU provide debugfs trace
5	output that summarizes counters and state.  This information is useful for
6	debugging RCU itself, and can sometimes also help to debug abuses of RCU.
7	The following sections describe the debugfs files and formats, first
8	for rcutree and next for rcutiny.
9	
10	
11	CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
12	
13	These implementations of RCU provide several debugfs directories under the
14	top-level directory "rcu":
15	
16	rcu/rcu_bh
17	rcu/rcu_preempt
18	rcu/rcu_sched
19	
20	Each directory contains files for the corresponding flavor of RCU.
21	Note that rcu/rcu_preempt is only present for CONFIG_TREE_PREEMPT_RCU.
22	For CONFIG_TREE_RCU, the RCU flavor maps onto the RCU-sched flavor,
23	so that activity for both appears in rcu/rcu_sched.
24	
25	In addition, the following file appears in the top-level directory:
26	rcu/rcutorture.  This file displays rcutorture test progress.  The output
27	of "cat rcu/rcutorture" looks as follows:
28	
29	rcutorture test sequence: 0 (test in progress)
30	rcutorture update version number: 615
31	
32	The first line shows the number of rcutorture tests that have completed
33	since boot.  If a test is currently running, the "(test in progress)"
34	string will appear as shown above.  The second line shows the number of
35	update cycles that the current test has started, or zero if there is
36	no test in progress.
37	
38	
39	Within each flavor directory (rcu/rcu_bh, rcu/rcu_sched, and possibly
40	also rcu/rcu_preempt) the following files will be present:
41	
42	rcudata:
43		Displays fields in struct rcu_data.
44	rcuexp:
45		Displays statistics for expedited grace periods.
46	rcugp:
47		Displays grace-period counters.
48	rcuhier:
49		Displays the struct rcu_node hierarchy.
50	rcu_pending:
51		Displays counts of the reasons rcu_pending() decided that RCU had
52		work to do.
53	rcuboost:
54		Displays RCU boosting statistics.  Only present if
55		CONFIG_RCU_BOOST=y.
56	
57	The output of "cat rcu/rcu_preempt/rcudata" looks as follows:
58	
59	  0!c=30455 g=30456 pq=1 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
60	  1!c=30719 g=30720 pq=1 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
61	  2!c=30150 g=30151 pq=1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
62	  3 c=31249 g=31250 pq=1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
63	  4!c=29502 g=29503 pq=1 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
64	  5 c=31201 g=31202 pq=1 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
65	  6!c=30253 g=30254 pq=1 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
66	  7 c=31178 g=31178 pq=1 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969
67	
68	This file has one line per CPU, or eight for this 8-CPU system.
69	The fields are as follows:
70	
71	o	The number at the beginning of each line is the CPU number.
72		CPUs numbers followed by an exclamation mark are offline,
73		but have been online at least once since boot.	There will be
74		no output for CPUs that have never been online, which can be
75		a good thing in the surprisingly common case where NR_CPUS is
76		substantially larger than the number of actual CPUs.
77	
78	o	"c" is the count of grace periods that this CPU believes have
79		completed.  Offlined CPUs and CPUs in dynticks idle mode may lag
80		quite a ways behind, for example, CPU 4 under "rcu_sched" above,
81		which has been offline through 16 RCU grace periods.  It is not
82		unusual to see offline CPUs lagging by thousands of grace periods.
83		Note that although the grace-period number is an unsigned long,
84		it is printed out as a signed long to allow more human-friendly
85		representation near boot time.
86	
87	o	"g" is the count of grace periods that this CPU believes have
88		started.  Again, offlined CPUs and CPUs in dynticks idle mode
89		may lag behind.  If the "c" and "g" values are equal, this CPU
90		has already reported a quiescent state for the last RCU grace
91		period that it is aware of, otherwise, the CPU believes that it
92		owes RCU a quiescent state.
93	
94	o	"pq" indicates that this CPU has passed through a quiescent state
95		for the current grace period.  It is possible for "pq" to be
96		"1" and "c" different than "g", which indicates that although
97		the CPU has passed through a quiescent state, either (1) this
98		CPU has not yet reported that fact, (2) some other CPU has not
99		yet reported for this grace period, or (3) both.
100	
101	o	"qp" indicates that RCU still expects a quiescent state from
102		this CPU.  Offlined CPUs and CPUs in dyntick idle mode might
103		well have qp=1, which is OK: RCU is still ignoring them.
104	
105	o	"dt" is the current value of the dyntick counter that is incremented
106		when entering or leaving idle, either due to a context switch or
107		due to an interrupt.  This number is even if the CPU is in idle
108		from RCU's viewpoint and odd otherwise.  The number after the
109		first "/" is the interrupt nesting depth when in idle state,
110		or a large number added to the interrupt-nesting depth when
111		running a non-idle task.  Some architectures do not accurately
112		count interrupt nesting when running in non-idle kernel context,
113		which can result in interesting anomalies such as negative
114		interrupt-nesting levels.  The number after the second "/"
115		is the NMI nesting depth.
116	
117	o	"df" is the number of times that some other CPU has forced a
118		quiescent state on behalf of this CPU due to this CPU being in
119		idle state.
120	
121	o	"of" is the number of times that some other CPU has forced a
122		quiescent state on behalf of this CPU due to this CPU being
123		offline.  In a perfect world, this might never happen, but it
124		turns out that offlining and onlining a CPU can take several grace
125		periods, and so there is likely to be an extended period of time
126		when RCU believes that the CPU is online when it really is not.
127		Please note that erring in the other direction (RCU believing a
128		CPU is offline when it is really alive and kicking) is a fatal
129		error, so it makes sense to err conservatively.
130	
131	o	"ql" is the number of RCU callbacks currently residing on
132		this CPU.  The first number is the number of "lazy" callbacks
133		that are known to RCU to only be freeing memory, and the number
134		after the "/" is the total number of callbacks, lazy or not.
135		These counters count callbacks regardless of what phase of
136		grace-period processing that they are in (new, waiting for
137		grace period to start, waiting for grace period to end, ready
138		to invoke).
139	
140	o	"qs" gives an indication of the state of the callback queue
141		with four characters:
142	
143		"N"	Indicates that there are callbacks queued that are not
144			ready to be handled by the next grace period, and thus
145			will be handled by the grace period following the next
146			one.
147	
148		"R"	Indicates that there are callbacks queued that are
149			ready to be handled by the next grace period.
150	
151		"W"	Indicates that there are callbacks queued that are
152			waiting on the current grace period.
153	
154		"D"	Indicates that there are callbacks queued that have
155			already been handled by a prior grace period, and are
156			thus waiting to be invoked.  Note that callbacks in
157			the process of being invoked are not counted here.
158			Callbacks in the process of being invoked are those
159			that have been removed from the rcu_data structures
160			queues by rcu_do_batch(), but which have not yet been
161			invoked.
162	
163		If there are no callbacks in a given one of the above states,
164		the corresponding character is replaced by ".".
165	
166	o	"b" is the batch limit for this CPU.  If more than this number
167		of RCU callbacks is ready to invoke, then the remainder will
168		be deferred.
169	
170	o	"ci" is the number of RCU callbacks that have been invoked for
171		this CPU.  Note that ci+nci+ql is the number of callbacks that have
172		been registered in absence of CPU-hotplug activity.
173	
174	o	"nci" is the number of RCU callbacks that have been offloaded from
175		this CPU.  This will always be zero unless the kernel was built
176		with CONFIG_RCU_NOCB_CPU=y and the "rcu_nocbs=" kernel boot
177		parameter was specified.
178	
179	o	"co" is the number of RCU callbacks that have been orphaned due to
180		this CPU going offline.  These orphaned callbacks have been moved
181		to an arbitrarily chosen online CPU.
182	
183	o	"ca" is the number of RCU callbacks that have been adopted by this
184		CPU due to other CPUs going offline.  Note that ci+co-ca+ql is
185		the number of RCU callbacks registered on this CPU.
186	
187	
188	Kernels compiled with CONFIG_RCU_BOOST=y display the following from
189	/debug/rcu/rcu_preempt/rcudata:
190	
191	  0!c=12865 g=12866 pq=1 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
192	  1 c=14407 g=14408 pq=1 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
193	  2 c=14407 g=14408 pq=1 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
194	  3 c=14407 g=14408 pq=1 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
195	  4 c=14405 g=14406 pq=1 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
196	  5!c=14168 g=14169 pq=1 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
197	  6 c=14404 g=14405 pq=1 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
198	  7 c=14407 g=14408 pq=1 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042
199	
200	This is similar to the output discussed above, but contains the following
201	additional fields:
202	
203	o	"kt" is the per-CPU kernel-thread state.  The digit preceding
204		the first slash is zero if there is no work pending and 1
205		otherwise.  The character between the first pair of slashes is
206		as follows:
207	
208		"S"	The kernel thread is stopped, in other words, all
209			CPUs corresponding to this rcu_node structure are
210			offline.
211	
212		"R"	The kernel thread is running.
213	
214		"W"	The kernel thread is waiting because there is no work
215			for it to do.
216	
217		"O"	The kernel thread is waiting because it has been
218			forced off of its designated CPU or because its
219			->cpus_allowed mask permits it to run on other than
220			its designated CPU.
221	
222		"Y"	The kernel thread is yielding to avoid hogging CPU.
223	
224		"?"	Unknown value, indicates a bug.
225	
226		The number after the final slash is the CPU that the kthread
227		is actually running on.
228	
229		This field is displayed only for CONFIG_RCU_BOOST kernels.
230	
231	o	"ktl" is the low-order 16 bits (in hexadecimal) of the count of
232		the number of times that this CPU's per-CPU kthread has gone
233		through its loop servicing invoke_rcu_cpu_kthread() requests.
234	
235		This field is displayed only for CONFIG_RCU_BOOST kernels.
236	
237	
238	The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
239	
240	s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
241	
242	These fields are as follows:
243	
244	o	"s" is the starting sequence number.
245	
246	o	"d" is the ending sequence number.  When the starting and ending
247		numbers differ, there is an expedited grace period in progress.
248	
249	o	"w" is the number of times that the sequence numbers have been
250		in danger of wrapping.
251	
252	o	"tf" is the number of times that contention has resulted in a
253		failure to begin an expedited grace period.
254	
255	o	"wd1" and "wd2" are the number of times that an attempt to
256		start an expedited grace period found that someone else had
257		completed an expedited grace period that satisfies the
258		attempted request.  "Our work is done."
259	
260	o	"n" is number of times that contention was so great that
261		the request was demoted from an expedited grace period to
262		a normal grace period.
263	
264	o	"sc" is the number of times that the attempt to start a
265		new expedited grace period succeeded.
266	
267	o	"dt" is the number of times that we attempted to update
268		the "d" counter.
269	
270	o	"dl" is the number of times that we failed to update the "d"
271		counter.
272	
273	o	"dx" is the number of times that we succeeded in updating
274		the "d" counter.
275	
276	
277	The output of "cat rcu/rcu_preempt/rcugp" looks as follows:
278	
279	completed=31249  gpnum=31250  age=1  max=18
280	
281	These fields are taken from the rcu_state structure, and are as follows:
282	
283	o	"completed" is the number of grace periods that have completed.
284		It is comparable to the "c" field from rcu/rcudata in that a
285		CPU whose "c" field matches the value of "completed" is aware
286		that the corresponding RCU grace period has completed.
287	
288	o	"gpnum" is the number of grace periods that have started.  It is
289		similarly comparable to the "g" field from rcu/rcudata in that
290		a CPU whose "g" field matches the value of "gpnum" is aware that
291		the corresponding RCU grace period has started.
292	
293		If these two fields are equal, then there is no grace period
294		in progress, in other words, RCU is idle.  On the other hand,
295		if the two fields differ (as they are above), then an RCU grace
296		period is in progress.
297	
298	o	"age" is the number of jiffies that the current grace period
299		has extended for, or zero if there is no grace period currently
300		in effect.
301	
302	o	"max" is the age in jiffies of the longest-duration grace period
303		thus far.
304	
305	The output of "cat rcu/rcu_preempt/rcuhier" looks as follows:
306	
307	c=14407 g=14408 s=0 jfq=2 j=c863 nfqs=12040/nfqsng=0(12040) fqlh=1051 oqlen=0/0
308	3/3 ..>. 0:7 ^0
309	e/e ..>. 0:3 ^0    d/d ..>. 4:7 ^1
310	
311	The fields are as follows:
312	
313	o	"c" is exactly the same as "completed" under rcu/rcu_preempt/rcugp.
314	
315	o	"g" is exactly the same as "gpnum" under rcu/rcu_preempt/rcugp.
316	
317	o	"s" is the current state of the force_quiescent_state()
318		state machine.
319	
320	o	"jfq" is the number of jiffies remaining for this grace period
321		before force_quiescent_state() is invoked to help push things
322		along.	Note that CPUs in idle mode throughout the grace period
323		will not report on their own, but rather must be check by some
324		other CPU via force_quiescent_state().
325	
326	o	"j" is the low-order four hex digits of the jiffies counter.
327		Yes, Paul did run into a number of problems that turned out to
328		be due to the jiffies counter no longer counting.  Why do you ask?
329	
330	o	"nfqs" is the number of calls to force_quiescent_state() since
331		boot.
332	
333	o	"nfqsng" is the number of useless calls to force_quiescent_state(),
334		where there wasn't actually a grace period active.  This can
335		no longer happen due to grace-period processing being pushed
336		into a kthread.  The number in parentheses is the difference
337		between "nfqs" and "nfqsng", or the number of times that
338		force_quiescent_state() actually did some real work.
339	
340	o	"fqlh" is the number of calls to force_quiescent_state() that
341		exited immediately (without even being counted in nfqs above)
342		due to contention on ->fqslock.
343	
344	o	Each element of the form "3/3 ..>. 0:7 ^0" represents one rcu_node
345		structure.  Each line represents one level of the hierarchy,
346		from root to leaves.  It is best to think of the rcu_data
347		structures as forming yet another level after the leaves.
348		Note that there might be either one, two, three, or even four
349		levels of rcu_node structures, depending on the relationship
350		between CONFIG_RCU_FANOUT, CONFIG_RCU_FANOUT_LEAF (possibly
351		adjusted using the rcu_fanout_leaf kernel boot parameter), and
352		CONFIG_NR_CPUS (possibly adjusted using the nr_cpu_ids count of
353		possible CPUs for the booting hardware).
354	
355		o	The numbers separated by the "/" are the qsmask followed
356			by the qsmaskinit.  The qsmask will have one bit
357			set for each entity in the next lower level that has
358			not yet checked in for the current grace period ("e"
359			indicating CPUs 5, 6, and 7 in the example above).
360			The qsmaskinit will have one bit for each entity that is
361			currently expected to check in during each grace period.
362			The value of qsmaskinit is assigned to that of qsmask
363			at the beginning of each grace period.
364	
365		o	The characters separated by the ">" indicate the state
366			of the blocked-tasks lists.  A "G" preceding the ">"
367			indicates that at least one task blocked in an RCU
368			read-side critical section blocks the current grace
369			period, while a "E" preceding the ">" indicates that
370			at least one task blocked in an RCU read-side critical
371			section blocks the current expedited grace period.
372			A "T" character following the ">" indicates that at
373			least one task is blocked within an RCU read-side
374			critical section, regardless of whether any current
375			grace period (expedited or normal) is inconvenienced.
376			A "." character appears if the corresponding condition
377			does not hold, so that "..>." indicates that no tasks
378			are blocked.  In contrast, "GE>T" indicates maximal
379			inconvenience from blocked tasks.  CONFIG_TREE_RCU
380			builds of the kernel will always show "..>.".
381	
382		o	The numbers separated by the ":" are the range of CPUs
383			served by this struct rcu_node.  This can be helpful
384			in working out how the hierarchy is wired together.
385	
386			For example, the example rcu_node structure shown above
387			has "0:7", indicating that it covers CPUs 0 through 7.
388	
389		o	The number after the "^" indicates the bit in the
390			next higher level rcu_node structure that this rcu_node
391			structure corresponds to.  For example, the "d/d ..>. 4:7
392			^1" has a "1" in this position, indicating that it
393			corresponds to the "1" bit in the "3" shown in the
394			"3/3 ..>. 0:7 ^0" entry on the next level up.
395	
396	
397	The output of "cat rcu/rcu_sched/rcu_pending" looks as follows:
398	
399	  0!np=26111 qsp=29 rpq=5386 cbr=1 cng=570 gpc=3674 gps=577 nn=15903 ndw=0
400	  1!np=28913 qsp=35 rpq=6097 cbr=1 cng=448 gpc=3700 gps=554 nn=18113 ndw=0
401	  2!np=32740 qsp=37 rpq=6202 cbr=0 cng=476 gpc=4627 gps=546 nn=20889 ndw=0
402	  3 np=23679 qsp=22 rpq=5044 cbr=1 cng=415 gpc=3403 gps=347 nn=14469 ndw=0
403	  4!np=30714 qsp=4 rpq=5574 cbr=0 cng=528 gpc=3931 gps=639 nn=20042 ndw=0
404	  5 np=28910 qsp=2 rpq=5246 cbr=0 cng=428 gpc=4105 gps=709 nn=18422 ndw=0
405	  6!np=38648 qsp=5 rpq=7076 cbr=0 cng=840 gpc=4072 gps=961 nn=25699 ndw=0
406	  7 np=37275 qsp=2 rpq=6873 cbr=0 cng=868 gpc=3416 gps=971 nn=25147 ndw=0
407	
408	The fields are as follows:
409	
410	o	The leading number is the CPU number, with "!" indicating
411		an offline CPU.
412	
413	o	"np" is the number of times that __rcu_pending() has been invoked
414		for the corresponding flavor of RCU.
415	
416	o	"qsp" is the number of times that the RCU was waiting for a
417		quiescent state from this CPU.
418	
419	o	"rpq" is the number of times that the CPU had passed through
420		a quiescent state, but not yet reported it to RCU.
421	
422	o	"cbr" is the number of times that this CPU had RCU callbacks
423		that had passed through a grace period, and were thus ready
424		to be invoked.
425	
426	o	"cng" is the number of times that this CPU needed another
427		grace period while RCU was idle.
428	
429	o	"gpc" is the number of times that an old grace period had
430		completed, but this CPU was not yet aware of it.
431	
432	o	"gps" is the number of times that a new grace period had started,
433		but this CPU was not yet aware of it.
434	
435	o	"ndw" is the number of times that a wakeup of an rcuo
436		callback-offload kthread had to be deferred in order to avoid
437		deadlock.
438	
439	o	"nn" is the number of times that this CPU needed nothing.
440	
441	
442	The output of "cat rcu/rcuboost" looks as follows:
443	
444	0:3 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
445	    balk: nt=0 egt=4695 bt=0 nb=0 ny=56 nos=0
446	4:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
447	    balk: nt=0 egt=6541 bt=0 nb=0 ny=126 nos=0
448	
449	This information is output only for rcu_preempt.  Each two-line entry
450	corresponds to a leaf rcu_node structure.  The fields are as follows:
451	
452	o	"n:m" is the CPU-number range for the corresponding two-line
453		entry.  In the sample output above, the first entry covers
454		CPUs zero through three and the second entry covers CPUs four
455		through seven.
456	
457	o	"tasks=TNEB" gives the state of the various segments of the
458		rnp->blocked_tasks list:
459	
460		"T"	This indicates that there are some tasks that blocked
461			while running on one of the corresponding CPUs while
462			in an RCU read-side critical section.
463	
464		"N"	This indicates that some of the blocked tasks are preventing
465			the current normal (non-expedited) grace period from
466			completing.
467	
468		"E"	This indicates that some of the blocked tasks are preventing
469			the current expedited grace period from completing.
470	
471		"B"	This indicates that some of the blocked tasks are in
472			need of RCU priority boosting.
473	
474		Each character is replaced with "." if the corresponding
475		condition does not hold.
476	
477	o	"kt" is the state of the RCU priority-boosting kernel
478		thread associated with the corresponding rcu_node structure.
479		The state can be one of the following:
480	
481		"S"	The kernel thread is stopped, in other words, all
482			CPUs corresponding to this rcu_node structure are
483			offline.
484	
485		"R"	The kernel thread is running.
486	
487		"W"	The kernel thread is waiting because there is no work
488			for it to do.
489	
490		"Y"	The kernel thread is yielding to avoid hogging CPU.
491	
492		"?"	Unknown value, indicates a bug.
493	
494	o	"ntb" is the number of tasks boosted.
495	
496	o	"neb" is the number of tasks boosted in order to complete an
497		expedited grace period.
498	
499	o	"nnb" is the number of tasks boosted in order to complete a
500		normal (non-expedited) grace period.  When boosting a task
501		that was blocking both an expedited and a normal grace period,
502		it is counted against the expedited total above.
503	
504	o	"j" is the low-order 16 bits of the jiffies counter in
505		hexadecimal.
506	
507	o	"bt" is the low-order 16 bits of the value that the jiffies
508		counter will have when we next start boosting, assuming that
509		the current grace period does not end beforehand.  This is
510		also in hexadecimal.
511	
512	o	"balk: nt" counts the number of times we didn't boost (in
513		other words, we balked) even though it was time to boost because
514		there were no blocked tasks to boost.  This situation occurs
515		when there is one blocked task on one rcu_node structure and
516		none on some other rcu_node structure.
517	
518	o	"egt" counts the number of times we balked because although
519		there were blocked tasks, none of them were blocking the
520		current grace period, whether expedited or otherwise.
521	
522	o	"bt" counts the number of times we balked because boosting
523		had already been initiated for the current grace period.
524	
525	o	"nb" counts the number of times we balked because there
526		was at least one task blocking the current non-expedited grace
527		period that never had blocked.  If it is already running, it
528		just won't help to boost its priority!
529	
530	o	"ny" counts the number of times we balked because it was
531		not yet time to start boosting.
532	
533	o	"nos" counts the number of times we balked for other
534		reasons, e.g., the grace period ended first.
535	
536	
537	CONFIG_TINY_RCU debugfs Files and Formats
538	
539	These implementations of RCU provides a single debugfs file under the
540	top-level directory RCU, namely rcu/rcudata, which displays fields in
541	rcu_bh_ctrlblk and rcu_sched_ctrlblk.
542	
543	The output of "cat rcu/rcudata" is as follows:
544	
545	rcu_sched: qlen: 0
546	rcu_bh: qlen: 0
547	
548	This is split into rcu_sched and rcu_bh sections.  The field is as
549	follows:
550	
551	o	"qlen" is the number of RCU callbacks currently waiting either
552		for an RCU grace period or waiting to be invoked.  This is the
553		only field present for rcu_sched and rcu_bh, due to the
554		short-circuiting of grace period in those two cases.
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