555 lines
22 KiB
Plaintext
Executable File
555 lines
22 KiB
Plaintext
Executable File
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 ndw=0
|
|
1!np=28913 qsp=35 rpq=6097 cbr=1 cng=448 gpc=3700 gps=554 nn=18113 ndw=0
|
|
2!np=32740 qsp=37 rpq=6202 cbr=0 cng=476 gpc=4627 gps=546 nn=20889 ndw=0
|
|
3 np=23679 qsp=22 rpq=5044 cbr=1 cng=415 gpc=3403 gps=347 nn=14469 ndw=0
|
|
4!np=30714 qsp=4 rpq=5574 cbr=0 cng=528 gpc=3931 gps=639 nn=20042 ndw=0
|
|
5 np=28910 qsp=2 rpq=5246 cbr=0 cng=428 gpc=4105 gps=709 nn=18422 ndw=0
|
|
6!np=38648 qsp=5 rpq=7076 cbr=0 cng=840 gpc=4072 gps=961 nn=25699 ndw=0
|
|
7 np=37275 qsp=2 rpq=6873 cbr=0 cng=868 gpc=3416 gps=971 nn=25147 ndw=0
|
|
|
|
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 "ndw" is the number of times that a wakeup of an rcuo
|
|
callback-offload kthread had to be deferred in order to avoid
|
|
deadlock.
|
|
|
|
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 structure. 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 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 and rcu_sched_ctrlblk.
|
|
|
|
The output of "cat rcu/rcudata" is as follows:
|
|
|
|
rcu_sched: qlen: 0
|
|
rcu_bh: qlen: 0
|
|
|
|
This is split into rcu_sched and rcu_bh sections. The field is 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.
|