CONFIG_RCU_TRACE debugfs Files and Formats
-The rcupreempt and rcutree 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.
-Note that the rcuclassic implementation of RCU does not provide debugfs
-trace output.
-
-The following sections describe the debugfs files and formats for
-preemptable RCU (rcupreempt) and hierarchical RCU (rcutree).
-
-
-Preemptable RCU debugfs Files and Formats
-
-This implementation of RCU provides three debugfs files under the
-top-level directory RCU: rcu/rcuctrs (which displays the per-CPU
-counters used by preemptable RCU) rcu/rcugp (which displays grace-period
-counters), and rcu/rcustats (which internal counters for debugging RCU).
-
-The output of "cat rcu/rcuctrs" looks as follows:
-
-CPU last cur F M
- 0 5 -5 0 0
- 1 -1 0 0 0
- 2 0 1 0 0
- 3 0 1 0 0
- 4 0 1 0 0
- 5 0 1 0 0
- 6 0 2 0 0
- 7 0 -1 0 0
- 8 0 1 0 0
-ggp = 26226, state = waitzero
-
-The per-CPU fields are as follows:
-
-o "CPU" gives the CPU number. Offline CPUs are not displayed.
-
-o "last" gives the value of the counter that is being decremented
- for the current grace period phase. In the example above,
- the counters sum to 4, indicating that there are still four
- RCU read-side critical sections still running that started
- before the last counter flip.
-
-o "cur" gives the value of the counter that is currently being
- both incremented (by rcu_read_lock()) and decremented (by
- rcu_read_unlock()). In the example above, the counters sum to
- 1, indicating that there is only one RCU read-side critical section
- still running that started after the last counter flip.
-
-o "F" indicates whether RCU is waiting for this CPU to acknowledge
- a counter flip. In the above example, RCU is not waiting on any,
- which is consistent with the state being "waitzero" rather than
- "waitack".
-
-o "M" indicates whether RCU is waiting for this CPU to execute a
- memory barrier. In the above example, RCU is not waiting on any,
- which is consistent with the state being "waitzero" rather than
- "waitmb".
-
-o "ggp" is the global grace-period counter.
-
-o "state" is the RCU state, which can be one of the following:
-
- o "idle": there is no grace period in progress.
-
- o "waitack": RCU just incremented the global grace-period
- counter, which has the effect of reversing the roles of
- the "last" and "cur" counters above, and is waiting for
- all the CPUs to acknowledge the flip. Once the flip has
- been acknowledged, CPUs will no longer be incrementing
- what are now the "last" counters, so that their sum will
- decrease monotonically down to zero.
-
- o "waitzero": RCU is waiting for the sum of the "last" counters
- to decrease to zero.
-
- o "waitmb": RCU is waiting for each CPU to execute a memory
- barrier, which ensures that instructions from a given CPU's
- last RCU read-side critical section cannot be reordered
- with instructions following the memory-barrier instruction.
-
-The output of "cat rcu/rcugp" looks as follows:
-
-oldggp=48870 newggp=48873
-
-Note that reading from this file provokes a synchronize_rcu(). The
-"oldggp" value is that of "ggp" from rcu/rcuctrs above, taken before
-executing the synchronize_rcu(), and the "newggp" value is also the
-"ggp" value, but taken after the synchronize_rcu() command returns.
-
-
-The output of "cat rcu/rcugp" looks as follows:
-
-na=1337955 nl=40 wa=1337915 wl=44 da=1337871 dl=0 dr=1337871 di=1337871
-1=50989 e1=6138 i1=49722 ie1=82 g1=49640 a1=315203 ae1=265563 a2=49640
-z1=1401244 ze1=1351605 z2=49639 m1=5661253 me1=5611614 m2=49639
-
-These are counters tracking internal preemptable-RCU events, however,
-some of them may be useful for debugging algorithms using RCU. In
-particular, the "nl", "wl", and "dl" values track the number of RCU
-callbacks in various states. The fields are as follows:
-
-o "na" is the total number of RCU callbacks that have been enqueued
- since boot.
-
-o "nl" is the number of RCU callbacks waiting for the previous
- grace period to end so that they can start waiting on the next
- grace period.
-
-o "wa" is the total number of RCU callbacks that have started waiting
- for a grace period since boot. "na" should be roughly equal to
- "nl" plus "wa".
-
-o "wl" is the number of RCU callbacks currently waiting for their
- grace period to end.
-
-o "da" is the total number of RCU callbacks whose grace periods
- have completed since boot. "wa" should be roughly equal to
- "wl" plus "da".
-
-o "dr" is the total number of RCU callbacks that have been removed
- from the list of callbacks ready to invoke. "dr" should be roughly
- equal to "da".
-
-o "di" is the total number of RCU callbacks that have been invoked
- since boot. "di" should be roughly equal to "da", though some
- early versions of preemptable RCU had a bug so that only the
- last CPU's count of invocations was displayed, rather than the
- sum of all CPU's counts.
-
-o "1" is the number of calls to rcu_try_flip(). This should be
- roughly equal to the sum of "e1", "i1", "a1", "z1", and "m1"
- described below. In other words, the number of times that
- the state machine is visited should be equal to the sum of the
- number of times that each state is visited plus the number of
- times that the state-machine lock acquisition failed.
-
-o "e1" is the number of times that rcu_try_flip() was unable to
- acquire the fliplock.
-
-o "i1" is the number of calls to rcu_try_flip_idle().
-
-o "ie1" is the number of times rcu_try_flip_idle() exited early
- due to the calling CPU having no work for RCU.
-
-o "g1" is the number of times that rcu_try_flip_idle() decided
- to start a new grace period. "i1" should be roughly equal to
- "ie1" plus "g1".
-
-o "a1" is the number of calls to rcu_try_flip_waitack().
-
-o "ae1" is the number of times that rcu_try_flip_waitack() found
- that at least one CPU had not yet acknowledge the new grace period
- (AKA "counter flip").
-
-o "a2" is the number of time rcu_try_flip_waitack() found that
- all CPUs had acknowledged. "a1" should be roughly equal to
- "ae1" plus "a2". (This particular output was collected on
- a 128-CPU machine, hence the smaller-than-usual fraction of
- calls to rcu_try_flip_waitack() finding all CPUs having already
- acknowledged.)
-
-o "z1" is the number of calls to rcu_try_flip_waitzero().
-
-o "ze1" is the number of times that rcu_try_flip_waitzero() found
- that not all of the old RCU read-side critical sections had
- completed.
-
-o "z2" is the number of times that rcu_try_flip_waitzero() finds
- the sum of the counters equal to zero, in other words, that
- all of the old RCU read-side critical sections had completed.
- The value of "z1" should be roughly equal to "ze1" plus
- "z2".
-
-o "m1" is the number of calls to rcu_try_flip_waitmb().
-
-o "me1" is the number of times that rcu_try_flip_waitmb() finds
- that at least one CPU has not yet executed a memory barrier.
-
-o "m2" is the number of times that rcu_try_flip_waitmb() finds that
- all CPUs have executed a memory barrier.
+The rcutree implementation of RCU provides 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.
Hierarchical RCU debugfs Files and Formats
6 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=859/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
7 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3761/1 dn=0 df=15 of=0 ri=0 ql=0 b=10
-The first section lists the rcu_data structures for rcu, the second for
-rcu_bh. Each section has one line per CPU, or eight for this 8-CPU system.
-The fields are as follows:
+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,
o "c" is the count of grace periods that this CPU believes have
completed. CPUs in dynticks idle mode may lag quite a ways
- behind, for example, CPU 4 under "rcu" above, which has slept
- through the past 25 RCU grace periods. It is not unusual to
- see CPUs lagging by thousands of grace periods.
+ behind, for example, CPU 4 under "rcu_sched" above, which has
+ slept through the past 25 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, CPUs in dynticks idle mode may lag behind.
rcu_sched: completed=33062 gpnum=33063
rcu_bh: completed=464 gpnum=464
-Again, this output is for both "rcu" and "rcu_bh". The fields are
-taken from the rcu_state structure, and are as follows:
+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
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" above), then an RCU grace period is in progress.
+ 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
+c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 oqlen=0
+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
+c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0 oqlen=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" and "rcu_bh" portions. The fields are
-as follows:
+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.
exited immediately (without even being counted in nfqs above)
due to contention on ->fqslock.
+o "oqlen" is the number of callbacks on the "orphan" callback
+ list. RCU callbacks are placed on this list by CPUs going
+ offline, and are "adopted" either by the CPU helping the outgoing
+ CPU or by the next rcu_barrier*() call, whichever comes first.
+
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
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
The value of qsmaskinit is assigned to that of qsmask
at the beginning of each grace period.
- For example, for "rcu", 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.
+ 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 "T" preceding the ">"
+ indicates that at least one task blocked in an RCU
+ read-side critical section blocks the current grace
+ period, while a "." preceding the ">" indicates otherwise.
+ The character following the ">" indicates similarly for
+ the next grace period. A "T" should appear in this
+ field only for rcu-preempt.
o The numbers separated by the ":" are the range of CPUs
served by this struct rcu_node. This can be helpful
6 np=120834 qsp=9902 cbr=0 cng=0 gpc=6 gps=3 nf=2 nn=110921
7 np=144888 qsp=26336 cbr=0 cng=0 gpc=8 gps=2 nf=0 nn=118542
-As always, this is once again split into "rcu" and "rcu_bh" portions.
-The fields are as follows:
+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.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff