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-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 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=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
- 1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
- 2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
- 3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
- 4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
- 5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
- 6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
- 7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
-rcu_bh:
- 0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
- 1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
- 2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
- 3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
- 4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
- 5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
- 6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
- 7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 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
-additional section for rcu_preempt. Each section 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 6 under "rcu_sched"
- above, which has been offline through not quite 40,000 RCU grace
- periods. It is not unusual to see CPUs lagging by thousands of
- grace periods.
-
-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 "pgp" indicates which grace period the last-observed quiescent
- state for this CPU corresponds to. This is important for handling
- the race between CPU 0 reporting an extended dynticks-idle
- quiescent state for CPU 1 and CPU 1 suddenly waking up and
- reporting its own quiescent state. If CPU 1 was the last CPU
- for the current grace period, then the CPU that loses this race
- will attempt to incorrectly mark CPU 1 as having checked in for
- the next grace period!
-
-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 dynticks idle state, either by the
- scheduler or by irq. This number is even if the CPU is in
- dyntick idle mode and odd otherwise. The number after the first
- "/" is the interrupt nesting depth when in dyntick-idle state,
- or one greater than the interrupt-nesting depth otherwise.
- 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
- dynticks-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. This is the total number of callbacks, regardless
- of what state 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 "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.
-
-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+ql is the number of callbacks that have
- been registered in absence of CPU-hotplug activity.
-
-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 due to
- other CPUs going offline. Note that ci+co-ca+ql is the number of
- RCU callbacks registered on this CPU.
-
-There is also an rcu/rcudata.csv file with the same information in
-comma-separated-variable spreadsheet format.
-
-
-The output of "cat rcu/rcugp" looks as follows:
-
-rcu_sched: completed=33062 gpnum=33063
-rcu_bh: completed=464 gpnum=464
-
-Again, this output is for both "rcu_sched" and "rcu_bh". Note that
-kernels built with CONFIG_TREE_PREEMPT_RCU will have an additional
-"rcu_preempt" line. The 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
- 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 (as they are for "rcu_bh" above),
- 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
- do for "rcu_sched" above), then an RCU grace period is in progress.
-
-
-The output of "cat rcu/rcuhier" looks as follows, with very long lines:
-
-c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
-1/1 ..>. 0:127 ^0
-3/3 ..>. 0:35 ^0 0/0 ..>. 36:71 ^1 0/0 ..>. 72:107 ^2 0/0 ..>. 108:127 ^3
-3/3f ..>. 0:5 ^0 2/3 ..>. 6:11 ^1 0/0 ..>. 12:17 ^2 0/0 ..>. 18:23 ^3 0/0 ..>. 24:29 ^4 0/0 ..>. 30:35 ^5 0/0 ..>. 36:41 ^0 0/0 ..>. 42:47 ^1 0/0 ..>. 48:53 ^2 0/0 ..>. 54:59 ^3 0/0 ..>. 60:65 ^4 0/0 ..>. 66:71 ^5 0/0 ..>. 72:77 ^0 0/0 ..>. 78:83 ^1 0/0 ..>. 84:89 ^2 0/0 ..>. 90:95 ^3 0/0 ..>. 96:101 ^4 0/0 ..>. 102:107 ^5 0/0 ..>. 108:113 ^0 0/0 ..>. 114:119 ^1 0/0 ..>. 120:125 ^2 0/0 ..>. 126:127 ^3
-rcu_bh:
-c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
-0/1 ..>. 0:127 ^0
-0/3 ..>. 0:35 ^0 0/0 ..>. 36:71 ^1 0/0 ..>. 72:107 ^2 0/0 ..>. 108:127 ^3
-0/3f ..>. 0:5 ^0 0/3 ..>. 6:11 ^1 0/0 ..>. 12:17 ^2 0/0 ..>. 18:23 ^3 0/0 ..>. 24:29 ^4 0/0 ..>. 30:35 ^5 0/0 ..>. 36:41 ^0 0/0 ..>. 42:47 ^1 0/0 ..>. 48:53 ^2 0/0 ..>. 54:59 ^3 0/0 ..>. 60:65 ^4 0/0 ..>. 66:71 ^5 0/0 ..>. 72:77 ^0 0/0 ..>. 78:83 ^1 0/0 ..>. 84:89 ^2 0/0 ..>. 90:95 ^3 0/0 ..>. 96:101 ^4 0/0 ..>. 102:107 ^5 0/0 ..>. 108:113 ^0 0/0 ..>. 114:119 ^1 0/0 ..>. 120:125 ^2 0/0 ..>. 126:127 ^3
-
-This is once again split into "rcu_sched" and "rcu_bh" portions,
-and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
-"rcu_preempt" section. The fields are as follows:
-
-o "c" is exactly the same as "completed" under rcu/rcugp.
-
-o "g" is exactly the same as "gpnum" under rcu/rcugp.
-
-o "s" is the "signaled" state that drives force_quiescent_state()'s
- 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 dyntick-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
- happen due to races. 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 "1/1 0:127 ^0" represents one struct
- rcu_node. 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, or three levels of rcu_node structures,
- depending on the relationship between CONFIG_RCU_FANOUT and
- CONFIG_NR_CPUS.
-
- 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.
- 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.
-
- For example, for "rcu_sched", the qsmask of the first
- entry of the lowest level is 0x14, meaning that we
- are still waiting for CPUs 2 and 4 to check in for the
- current 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.
-
- 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 first entry at the lowest level shows
- "0:5", indicating that it covers CPUs 0 through 5.
-
- 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 first entry at the lowest level shows
- "^0", indicating that it corresponds to bit zero in
- the first entry at the middle level.
-
-
-The output of "cat rcu/rcu_pending" looks as follows:
-
-rcu_sched:
- 0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741
- 1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792
- 2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629
- 3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nf=207 nn=137723
- 4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nf=3529 nn=123110
- 5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nf=201 nn=137456
- 6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nf=4202 nn=120834
- 7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nf=41 nn=144888
-rcu_bh:
- 0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nf=2 nn=145314
- 1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nf=3 nn=143180
- 2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nf=0 nn=117936
- 3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nf=0 nn=134863
- 4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nf=0 nn=110671
- 5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nf=0 nn=133235
- 6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nf=2 nn=110921
- 7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nf=0 nn=118542
-
-As always, this is once again split into "rcu_sched" and "rcu_bh"
-portions, with CONFIG_TREE_PREEMPT_RCU kernels having an additional
-"rcu_preempt" section. The fields are as follows:
-
-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 "nf" is the number of times that this CPU suspected that the
- current grace period had run for too long, and thus needed to
- be forced.
-
- Please note that "forcing" consists of sending resched IPIs
- to holdout CPUs. If that CPU really still is in an old RCU
- read-side critical section, then we really do have to wait for it.
- The assumption behing "forcing" is that the CPU is not still in
- an old RCU read-side critical section, but has not yet responded
- for some other reason.
-
-o "nn" is the number of times that this CPU needed nothing. Alert
- readers will note that the rcu "nn" number for a given CPU very
- closely matches the rcu_bh "np" number for that same CPU. This
- 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
-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.