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Based on kernel version 3.9. Page generated on 2013-05-02 23:13 EST.

	CONFIG_RCU_TRACE debugfs Files and Formats
	
	
	The rcutree and rcutiny implementations of RCU provide debugfs trace
	output that summarizes counters and state.  This information is useful for
	debugging RCU itself, and can sometimes also help to debug abuses of RCU.
	The following sections describe the debugfs files and formats, first
	for rcutree and next for rcutiny.
	
	
	CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
	
	These implementations of RCU provide several debugfs directories under the
	top-level directory "rcu":
	
	rcu/rcu_bh
	rcu/rcu_preempt
	rcu/rcu_sched
	
	Each directory contains files for the corresponding flavor of RCU.
	Note that rcu/rcu_preempt is only present for CONFIG_TREE_PREEMPT_RCU.
	For CONFIG_TREE_RCU, the RCU flavor maps onto the RCU-sched flavor,
	so that activity for both appears in rcu/rcu_sched.
	
	In addition, the following file appears in the top-level directory:
	rcu/rcutorture.  This file displays rcutorture test progress.  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.
	
	
	Within each flavor directory (rcu/rcu_bh, rcu/rcu_sched, and possibly
	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:
		Displays the struct rcu_node hierarchy.
	rcu_pending:
		Displays counts of the reasons rcu_pending() decided that RCU had
		work to do.
	rcuboost:
		Displays RCU boosting statistics.  Only present if
		CONFIG_RCU_BOOST=y.
	
	The output of "cat rcu/rcu_preempt/rcudata" looks as follows:
	
	  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
	  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
	  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
	  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
	  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
	  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
	  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
	  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
	
	This file has one line per CPU, or eight for this 8-CPU system.
	The fields are as follows:
	
	o	The number at the beginning of each line is the CPU number.
		CPUs numbers followed by an exclamation mark are offline,
		but have been online at least once since boot.	There will be
		no output for CPUs that have never been online, which can be
		a good thing in the surprisingly common case where NR_CPUS is
		substantially larger than the number of actual CPUs.
	
	o	"c" is the count of grace periods that this CPU believes have
		completed.  Offlined CPUs and CPUs in dynticks idle mode may lag
		quite a ways behind, for example, CPU 4 under "rcu_sched" above,
		which has been offline through 16 RCU grace periods.  It is not
		unusual to see offline CPUs lagging by thousands of grace periods.
		Note that although the grace-period number is an unsigned long,
		it is printed out as a signed long to allow more human-friendly
		representation near boot time.
	
	o	"g" is the count of grace periods that this CPU believes have
		started.  Again, offlined CPUs and CPUs in dynticks idle mode
		may lag behind.  If the "c" and "g" values are equal, this CPU
		has already reported a quiescent state for the last RCU grace
		period that it is aware of, otherwise, the CPU believes that it
		owes RCU a quiescent state.
	
	o	"pq" indicates that this CPU has passed through a quiescent state
		for the current grace period.  It is possible for "pq" to be
		"1" and "c" different than "g", which indicates that although
		the CPU has passed through a quiescent state, either (1) this
		CPU has not yet reported that fact, (2) some other CPU has not
		yet reported for this grace period, or (3) both.
	
	o	"qp" indicates that RCU still expects a quiescent state from
		this CPU.  Offlined CPUs and CPUs in dyntick idle mode might
		well have qp=1, which is OK: RCU is still ignoring them.
	
	o	"dt" is the current value of the dyntick counter that is incremented
		when entering or leaving idle, either due to a context switch or
		due to an interrupt.  This number is even if the CPU is in idle
		from RCU's viewpoint and odd otherwise.  The number after the
		first "/" is the interrupt nesting depth when in idle state,
		or a large number added to the interrupt-nesting depth when
		running a non-idle task.  Some architectures do not accurately
		count interrupt nesting when running in non-idle kernel context,
		which can result in interesting anomalies such as negative
		interrupt-nesting levels.  The number after the second "/"
		is the NMI nesting depth.
	
	o	"df" is the number of times that some other CPU has forced a
		quiescent state on behalf of this CPU due to this CPU being in
		idle state.
	
	o	"of" is the number of times that some other CPU has forced a
		quiescent state on behalf of this CPU due to this CPU being
		offline.  In a perfect world, this might never happen, but it
		turns out that offlining and onlining a CPU can take several grace
		periods, and so there is likely to be an extended period of time
		when RCU believes that the CPU is online when it really is not.
		Please note that erring in the other direction (RCU believing a
		CPU is offline when it is really alive and kicking) is a fatal
		error, so it makes sense to err conservatively.
	
	o	"ql" is the number of RCU callbacks currently residing on
		this CPU.  The first number is the number of "lazy" callbacks
		that are known to RCU to only be freeing memory, and the number
		after the "/" is the total number of callbacks, lazy or not.
		These counters count callbacks regardless of what phase of
		grace-period processing that they are in (new, waiting for
		grace period to start, waiting for grace period to end, ready
		to invoke).
	
	o	"qs" gives an indication of the state of the callback queue
		with four characters:
	
		"N"	Indicates that there are callbacks queued that are not
			ready to be handled by the next grace period, and thus
			will be handled by the grace period following the next
			one.
	
		"R"	Indicates that there are callbacks queued that are
			ready to be handled by the next grace period.
	
		"W"	Indicates that there are callbacks queued that are
			waiting on the current grace period.
	
		"D"	Indicates that there are callbacks queued that have
			already been handled by a prior grace period, and are
			thus waiting to be invoked.  Note that callbacks in
			the process of being invoked are not counted here.
			Callbacks in the process of being invoked are those
			that have been removed from the rcu_data structures
			queues by rcu_do_batch(), but which have not yet been
			invoked.
	
		If there are no callbacks in a given one of the above states,
		the corresponding character is replaced by ".".
	
	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.
	
	o	"ci" is the number of RCU callbacks that have been invoked for
		this CPU.  Note that ci+nci+ql is the number of callbacks that have
		been registered in absence of CPU-hotplug activity.
	
	o	"nci" is the number of RCU callbacks that have been offloaded from
		this CPU.  This will always be zero unless the kernel was built
		with CONFIG_RCU_NOCB_CPU=y and the "rcu_nocbs=" kernel boot
		parameter was specified.
	
	o	"co" is the number of RCU callbacks that have been orphaned due to
		this CPU going offline.  These orphaned callbacks have been moved
		to an arbitrarily chosen online CPU.
	
	o	"ca" is the number of RCU callbacks that have been adopted by this
		CPU due to other CPUs going offline.  Note that ci+co-ca+ql is
		the number of RCU callbacks registered on this CPU.
	
	
	Kernels compiled with CONFIG_RCU_BOOST=y display the following from
	/debug/rcu/rcu_preempt/rcudata:
	
	  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
	  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
	  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
	  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
	  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
	  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
	  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
	  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
	
	This is similar to the output discussed above, but contains the following
	additional fields:
	
	o	"kt" is the per-CPU kernel-thread state.  The digit preceding
		the first slash is zero if there is no work pending and 1
		otherwise.  The character between the first pair of slashes 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.
	
		"O"	The kernel thread is waiting because it has been
			forced off of its designated CPU or because its
			->cpus_allowed mask permits it to run on other than
			its designated CPU.
	
		"Y"	The kernel thread is yielding to avoid hogging CPU.
	
		"?"	Unknown value, indicates a bug.
	
		The number after the final slash is the CPU that the kthread
		is actually running on.
	
		This field is displayed only for CONFIG_RCU_BOOST kernels.
	
	o	"ktl" is the low-order 16 bits (in hexadecimal) of the count of
		the number of times that this CPU's per-CPU kthread has gone
		through its loop servicing invoke_rcu_cpu_kthread() requests.
	
		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
	
	These fields are taken from the rcu_state structure, and are as follows:
	
	o	"completed" is the number of grace periods that have completed.
		It is comparable to the "c" field from rcu/rcudata in that a
		CPU whose "c" field matches the value of "completed" is aware
		that the corresponding RCU grace period has completed.
	
	o	"gpnum" is the number of grace periods that have started.  It is
		similarly comparable to the "g" field from rcu/rcudata in that
		a CPU whose "g" field matches the value of "gpnum" is aware that
		the corresponding RCU grace period has started.
	
		If these two fields are equal, then there is no grace period
		in progress, in other words, RCU is idle.  On the other hand,
		if the two fields differ (as they are above), then an RCU grace
		period is in progress.
	
	o	"age" is the number of jiffies that the current grace period
		has extended for, or zero if there is no grace period currently
		in effect.
	
	o	"max" is the age in jiffies of the longest-duration grace period
		thus far.
	
	The output of "cat rcu/rcu_preempt/rcuhier" looks as follows:
	
	c=14407 g=14408 s=0 jfq=2 j=c863 nfqs=12040/nfqsng=0(12040) fqlh=1051 oqlen=0/0
	3/3 ..>. 0:7 ^0
	e/e ..>. 0:3 ^0    d/d ..>. 4:7 ^1
	
	The fields are as follows:
	
	o	"c" is exactly the same as "completed" under rcu/rcu_preempt/rcugp.
	
	o	"g" is exactly the same as "gpnum" under rcu/rcu_preempt/rcugp.
	
	o	"s" is the current state of the force_quiescent_state()
		state machine.
	
	o	"jfq" is the number of jiffies remaining for this grace period
		before force_quiescent_state() is invoked to help push things
		along.	Note that CPUs in idle mode throughout the grace period
		will not report on their own, but rather must be check by some
		other CPU via force_quiescent_state().
	
	o	"j" is the low-order four hex digits of the jiffies counter.
		Yes, Paul did run into a number of problems that turned out to
		be due to the jiffies counter no longer counting.  Why do you ask?
	
	o	"nfqs" is the number of calls to force_quiescent_state() since
		boot.
	
	o	"nfqsng" is the number of useless calls to force_quiescent_state(),
		where there wasn't actually a grace period active.  This can
		no longer happen due to grace-period processing being pushed
		into a kthread.  The number in parentheses is the difference
		between "nfqs" and "nfqsng", or the number of times that
		force_quiescent_state() actually did some real work.
	
	o	"fqlh" is the number of calls to force_quiescent_state() that
		exited immediately (without even being counted in nfqs above)
		due to contention on ->fqslock.
	
	o	Each element of the form "3/3 ..>. 0:7 ^0" represents one rcu_node
		structure.  Each line represents one level of the hierarchy,
		from root to leaves.  It is best to think of the rcu_data
		structures as forming yet another level after the leaves.
		Note that there might be either one, two, three, or even four
		levels of rcu_node structures, depending on the relationship
		between CONFIG_RCU_FANOUT, CONFIG_RCU_FANOUT_LEAF (possibly
		adjusted using the rcu_fanout_leaf kernel boot parameter), and
		CONFIG_NR_CPUS (possibly adjusted using the nr_cpu_ids count of
		possible CPUs for the booting hardware).
	
		o	The numbers separated by the "/" are the qsmask followed
			by the qsmaskinit.  The qsmask will have one bit
			set for each entity in the next lower level that has
			not yet checked in for the current grace period ("e"
			indicating CPUs 5, 6, and 7 in the example above).
			The qsmaskinit will have one bit for each entity that is
			currently expected to check in during each grace period.
			The value of qsmaskinit is assigned to that of qsmask
			at the beginning of each grace period.
	
		o	The characters separated by the ">" indicate the state
			of the blocked-tasks lists.  A "G" preceding the ">"
			indicates that at least one task blocked in an RCU
			read-side critical section blocks the current grace
			period, while a "E" preceding the ">" indicates that
			at least one task blocked in an RCU read-side critical
			section blocks the current expedited grace period.
			A "T" character following the ">" indicates that at
			least one task is blocked within an RCU read-side
			critical section, regardless of whether any current
			grace period (expedited or normal) is inconvenienced.
			A "." character appears if the corresponding condition
			does not hold, so that "..>." indicates that no tasks
			are blocked.  In contrast, "GE>T" indicates maximal
			inconvenience from blocked tasks.  CONFIG_TREE_RCU
			builds of the kernel will always show "..>.".
	
		o	The numbers separated by the ":" are the range of CPUs
			served by this struct rcu_node.  This can be helpful
			in working out how the hierarchy is wired together.
	
			For example, the example rcu_node structure shown above
			has "0:7", indicating that it covers CPUs 0 through 7.
	
		o	The number after the "^" indicates the bit in the
			next higher level rcu_node structure that this rcu_node
			structure corresponds to.  For example, the "d/d ..>. 4:7
			^1" has a "1" in this position, indicating that it
			corresponds to the "1" bit in the "3" shown in the
			"3/3 ..>. 0:7 ^0" entry on the next level up.
	
	
	The output of "cat rcu/rcu_sched/rcu_pending" looks as follows:
	
	  0!np=26111 qsp=29 rpq=5386 cbr=1 cng=570 gpc=3674 gps=577 nn=15903
	  1!np=28913 qsp=35 rpq=6097 cbr=1 cng=448 gpc=3700 gps=554 nn=18113
	  2!np=32740 qsp=37 rpq=6202 cbr=0 cng=476 gpc=4627 gps=546 nn=20889
	  3 np=23679 qsp=22 rpq=5044 cbr=1 cng=415 gpc=3403 gps=347 nn=14469
	  4!np=30714 qsp=4 rpq=5574 cbr=0 cng=528 gpc=3931 gps=639 nn=20042
	  5 np=28910 qsp=2 rpq=5246 cbr=0 cng=428 gpc=4105 gps=709 nn=18422
	  6!np=38648 qsp=5 rpq=7076 cbr=0 cng=840 gpc=4072 gps=961 nn=25699
	  7 np=37275 qsp=2 rpq=6873 cbr=0 cng=868 gpc=3416 gps=971 nn=25147
	
	The fields are as follows:
	
	o	The leading number is the CPU number, with "!" indicating
		an offline CPU.
	
	o	"np" is the number of times that __rcu_pending() has been invoked
		for the corresponding flavor of RCU.
	
	o	"qsp" is the number of times that the RCU was waiting for a
		quiescent state from this CPU.
	
	o	"rpq" is the number of times that the CPU had passed through
		a quiescent state, but not yet reported it to RCU.
	
	o	"cbr" is the number of times that this CPU had RCU callbacks
		that had passed through a grace period, and were thus ready
		to be invoked.
	
	o	"cng" is the number of times that this CPU needed another
		grace period while RCU was idle.
	
	o	"gpc" is the number of times that an old grace period had
		completed, but this CPU was not yet aware of it.
	
	o	"gps" is the number of times that a new grace period had started,
		but this CPU was not yet aware of it.
	
	o	"nn" is the number of times that this CPU needed nothing.
	
	
	The output of "cat rcu/rcuboost" looks as follows:
	
	0:3 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
	    balk: nt=0 egt=4695 bt=0 nb=0 ny=56 nos=0
	4:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
	    balk: nt=0 egt=6541 bt=0 nb=0 ny=126 nos=0
	
	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 three and the second entry covers CPUs four
		through seven.
	
	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
	top-level directory RCU, namely rcu/rcudata, which displays fields in
	rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
	rcu_preempt_ctrlblk.
	
	The output of "cat rcu/rcudata" is as follows:
	
	rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=...
	             ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274
	             normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0
	             exp balk: bt=0 nos=0
	rcu_sched: qlen: 0
	rcu_bh: qlen: 0
	
	This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the
	rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds.
	The last three lines of the rcu_preempt section appear only in
	CONFIG_RCU_BOOST kernel builds.  The fields are as follows:
	
	o	"qlen" is the number of RCU callbacks currently waiting either
		for an RCU grace period or waiting to be invoked.  This is the
		only field present for rcu_sched and rcu_bh, due to the
		short-circuiting of grace period in those two cases.
	
	o	"gp" is the number of grace periods that have completed.
	
	o	"g197/p197/c197" displays the grace-period state, with the
		"g" number being the number of grace periods that have started
		(mod 256), the "p" number being the number of grace periods
		that the CPU has responded to (also mod 256), and the "c"
		number being the number of grace periods that have completed
		(once again mode 256).
	
		Why have both "gp" and "g"?  Because the data flowing into
		"gp" is only present in a CONFIG_RCU_TRACE kernel.
	
	o	"tasks" is a set of bits.  The first bit is "T" if there are
		currently tasks that have recently blocked within an RCU
		read-side critical section, the second bit is "N" if any of the
		aforementioned tasks are blocking the current RCU grace period,
		and the third bit is "E" if any of the aforementioned tasks are
		blocking the current expedited grace period.  Each bit is "."
		if the corresponding condition does not hold.
	
	o	"ttb" is a single bit.  It is "B" if any of the blocked tasks
		need to be priority boosted and "." otherwise.
	
	o	"btg" indicates whether boosting has been carried out during
		the current grace period, with "exp" indicating that boosting
		is in progress for an expedited grace period, "no" indicating
		that boosting has not yet started for a normal grace period,
		"begun" indicating that boosting has bebug for a normal grace
		period, and "done" indicating that boosting has completed for
		a normal grace period.
	
	o	"ntb" is the total number of tasks subjected to RCU priority boosting
		periods since boot.
	
	o	"neb" is the number of expedited grace periods that have had
		to resort to RCU priority boosting since boot.
	
	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 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 at the next time that boosting is scheduled to begin.
	
	o	In the line beginning with "normal balk", the fields are as follows:
	
		o	"nt" is the number of times that the system balked from
			boosting because there were no blocked tasks to boost.
			Note that the system will balk from boosting even if the
			grace period is overdue when the currently running task
			is looping within an RCU read-side critical section.
			There is no point in boosting in this case, because
			boosting a running task won't make it run any faster.
	
		o	"gt" is the number of times that the system balked
			from boosting because, although there were blocked tasks,
			none of them were preventing the current grace period
			from completing.
	
		o	"bt" is the number of times that the system balked
			from boosting because boosting was already in progress.
	
		o	"b" is the number of times that the system balked from
			boosting because boosting had already completed for
			the grace period in question.
	
		o	"ny" is the number of times that the system balked from
			boosting because it was not yet time to start boosting
			the grace period in question.
	
		o	"nos" is the number of times that the system balked from
			boosting for inexplicable ("not otherwise specified")
			reasons.  This can actually happen due to races involving
			increments of the jiffies counter.
	
	o	In the line beginning with "exp balk", the fields are as follows:
	
		o	"bt" is the number of times that the system balked from
			boosting because there were no blocked tasks to boost.
	
		o	"nos" is the number of times that the system balked from
			 boosting for inexplicable ("not otherwise specified")
			 reasons.

• [ RCU ]
• 00-INDEX
• arrayRCU.txt
• checklist.txt
• listRCU.txt
• lockdep-splat.txt
• lockdep.txt
• NMI-RCU.txt
• rcu.txt
• rcubarrier.txt
• rculist_nulls.txt
• rcuref.txt
• RTFP.txt
• stallwarn.txt
• torture.txt
• trace.txt
• UP.txt
• whatisRCU.txt
•