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rcu: Update documentation for TREE_RCU debugfs tracing 

This commit updates the tracing documentation to reflect the new
format that has per-RCU-flavor directories.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-10-31 13:00:15 -07:00 committed by Paul E. McKenney
parent a4d611fdca
commit 40e80c469f
1 changed files with 176 additions and 177 deletions
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353
Documentation/RCU/trace.txt
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@ -10,51 +10,61 @@ for rcutree and next for rcutiny.
CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
These implementations of RCU provides several debugfs files under the These implementations of RCU provide several debugfs directories under the
top-level directory "rcu": top-level directory "rcu":
rcu/rcudata: 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. Displays fields in struct rcu_data.
rcu/rcudata.csv: rcugp:
Comma-separated values spreadsheet version of rcudata.
rcu/rcugp:
Displays grace-period counters. Displays grace-period counters.
rcu/rcuhier: rcuhier:
Displays the struct rcu_node hierarchy. Displays the struct rcu_node hierarchy.
rcu/rcu_pending: rcu_pending:
Displays counts of the reasons rcu_pending() decided that RCU had Displays counts of the reasons rcu_pending() decided that RCU had
work to do. work to do.
rcu/rcutorture: rcuboost:
Displays rcutorture test progress.
rcu/rcuboost:
Displays RCU boosting statistics. Only present if Displays RCU boosting statistics. Only present if
CONFIG_RCU_BOOST=y. CONFIG_RCU_BOOST=y.
The output of "cat rcu/rcudata" looks as follows: The output of "cat rcu/rcu_preempt/rcudata" looks as follows:
rcu_sched: 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
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=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
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=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
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=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
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=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
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=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
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=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
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=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
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 This file has one line per CPU, or eight for this 8-CPU system.
for rcu_bh. Note that CONFIG_TREE_PREEMPT_RCU kernels will have an The fields are as follows:
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. o The number at the beginning of each line is the CPU number.
CPUs numbers followed by an exclamation mark are offline, CPUs numbers followed by an exclamation mark are offline,
@ -64,11 +74,13 @@ o The number at the beginning of each line is the CPU number.
substantially larger than the number of actual CPUs. substantially larger than the number of actual CPUs.
o "c" is the count of grace periods that this CPU believes have o "c" is the count of grace periods that this CPU believes have
completed. Offlined CPUs and CPUs in dynticks idle mode may completed. Offlined CPUs and CPUs in dynticks idle mode may lag
lag quite a ways behind, for example, CPU 6 under "rcu_sched" quite a ways behind, for example, CPU 4 under "rcu_sched" above,
above, which has been offline through not quite 40,000 RCU grace which has been offline through 16 RCU grace periods. It is not
periods. It is not unusual to see CPUs lagging by thousands of unusual to see offline CPUs lagging by thousands of grace periods.
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 o "g" is the count of grace periods that this CPU believes have
started. Again, offlined CPUs and CPUs in dynticks idle mode started. Again, offlined CPUs and CPUs in dynticks idle mode
@ -84,30 +96,25 @@ o "pq" indicates that this CPU has passed through a quiescent state
CPU has not yet reported that fact, (2) some other CPU has not CPU has not yet reported that fact, (2) some other CPU has not
yet reported for this grace period, or (3) both. 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 o "qp" indicates that RCU still expects a quiescent state from
this CPU. Offlined CPUs and CPUs in dyntick idle mode might this CPU. Offlined CPUs and CPUs in dyntick idle mode might
well have qp=1, which is OK: RCU is still ignoring them. 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 o "dt" is the current value of the dyntick counter that is incremented
when entering or leaving dynticks idle state, either by the when entering or leaving idle, either due to a context switch or
scheduler or by irq. This number is even if the CPU is in due to an interrupt. This number is even if the CPU is in idle
dyntick idle mode and odd otherwise. The number after the first from RCU's viewpoint and odd otherwise. The number after the
"/" is the interrupt nesting depth when in dyntick-idle state, first "/" is the interrupt nesting depth when in idle state,
or one greater than the interrupt-nesting depth otherwise. or a large number added to the interrupt-nesting depth when
The number after the second "/" is the NMI nesting depth. 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 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 quiescent state on behalf of this CPU due to this CPU being in
dynticks-idle state. idle state.
o "of" is the number of times that some other CPU has forced a 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 quiescent state on behalf of this CPU due to this CPU being
@ -120,9 +127,13 @@ o "of" is the number of times that some other CPU has forced a
error, so it makes sense to err conservatively. error, so it makes sense to err conservatively.
o "ql" is the number of RCU callbacks currently residing on o "ql" is the number of RCU callbacks currently residing on
this CPU. This is the total number of callbacks, regardless this CPU. The first number is the number of "lazy" callbacks
of what state they are in (new, waiting for grace period to that are known to RCU to only be freeing memory, and the number
start, waiting for grace period to end, ready to invoke). 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 o "qs" gives an indication of the state of the callback queue
with four characters: with four characters:
@ -150,6 +161,43 @@ o "qs" gives an indication of the state of the callback queue
If there are no callbacks in a given one of the above states, If there are no callbacks in a given one of the above states,
the corresponding character is replaced by ".". 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 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 the first slash is zero if there is no work pending and 1
otherwise. The character between the first pair of slashes is otherwise. The character between the first pair of slashes is
@ -184,35 +232,12 @@ o "ktl" is the low-order 16 bits (in hexadecimal) of the count of
This field is displayed only for CONFIG_RCU_BOOST kernels. 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 The output of "cat rcu/rcu_preempt/rcugp" looks as follows:
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 completed=31249 gpnum=31250 age=1 max=18
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 These fields are taken from the rcu_state structure, and are as follows:
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. o "completed" is the number of grace periods that have completed.
It is comparable to the "c" field from rcu/rcudata in that a It is comparable to the "c" field from rcu/rcudata in that a
@ -220,44 +245,42 @@ o "completed" is the number of grace periods that have completed.
that the corresponding RCU grace period has completed. that the corresponding RCU grace period has completed.
o "gpnum" is the number of grace periods that have started. It is 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 similarly comparable to the "g" field from rcu/rcudata in that
whose "g" field matches the value of "gpnum" is aware that the a CPU whose "g" field matches the value of "gpnum" is aware that
corresponding RCU grace period has started. the corresponding RCU grace period has started.
If these two fields are equal (as they are for "rcu_bh" above), If these two fields are equal, then there is no grace period
then there is no grace period in progress, in other words, RCU in progress, in other words, RCU is idle. On the other hand,
is idle. On the other hand, if the two fields differ (as they if the two fields differ (as they are above), then an RCU grace
do for "rcu_sched" above), then an RCU grace period is in progress. 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.
The output of "cat rcu/rcuhier" looks as follows, with very long lines: o "max" is the age in jiffies of the longest-duration grace period
thus far.
c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6 The output of "cat rcu/rcu_preempt/rcuhier" looks as follows:
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, c=14407 g=14408 s=0 jfq=2 j=c863 nfqs=12040/nfqsng=0(12040) fqlh=1051 oqlen=0/0
and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional 3/3 ..>. 0:7 ^0
"rcu_preempt" section. The fields are as follows: e/e ..>. 0:3 ^0 d/d ..>. 4:7 ^1
o "c" is exactly the same as "completed" under rcu/rcugp. The fields are as follows:
o "g" is exactly the same as "gpnum" under rcu/rcugp. o "c" is exactly the same as "completed" under rcu/rcu_preempt/rcugp.
o "s" is the "signaled" state that drives force_quiescent_state()'s 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. state machine.
o "jfq" is the number of jiffies remaining for this grace period o "jfq" is the number of jiffies remaining for this grace period
before force_quiescent_state() is invoked to help push things before force_quiescent_state() is invoked to help push things
along. Note that CPUs in dyntick-idle mode throughout the grace along. Note that CPUs in idle mode throughout the grace period
period will not report on their own, but rather must be check by will not report on their own, but rather must be check by some
some other CPU via force_quiescent_state(). other CPU via force_quiescent_state().
o "j" is the low-order four hex digits of the jiffies counter. 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 Yes, Paul did run into a number of problems that turned out to
@ -268,7 +291,8 @@ o "nfqs" is the number of calls to force_quiescent_state() since
o "nfqsng" is the number of useless calls to force_quiescent_state(), o "nfqsng" is the number of useless calls to force_quiescent_state(),
where there wasn't actually a grace period active. This can where there wasn't actually a grace period active. This can
happen due to races. The number in parentheses is the difference 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 between "nfqs" and "nfqsng", or the number of times that
force_quiescent_state() actually did some real work. force_quiescent_state() actually did some real work.
@ -276,28 +300,27 @@ o "fqlh" is the number of calls to force_quiescent_state() that
exited immediately (without even being counted in nfqs above) exited immediately (without even being counted in nfqs above)
due to contention on ->fqslock. due to contention on ->fqslock.
o Each element of the form "1/1 0:127 ^0" represents one struct o Each element of the form "3/3 ..>. 0:7 ^0" represents one rcu_node
rcu_node. Each line represents one level of the hierarchy, from structure. Each line represents one level of the hierarchy,
root to leaves. It is best to think of the rcu_data structures from root to leaves. It is best to think of the rcu_data
as forming yet another level after the leaves. Note that there structures as forming yet another level after the leaves.
might be either one, two, or three levels of rcu_node structures, Note that there might be either one, two, three, or even four
depending on the relationship between CONFIG_RCU_FANOUT and levels of rcu_node structures, depending on the relationship
CONFIG_NR_CPUS. 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 o The numbers separated by the "/" are the qsmask followed
by the qsmaskinit. The qsmask will have one bit by the qsmaskinit. The qsmask will have one bit
set for each entity in the next lower level that set for each entity in the next lower level that has
has not yet checked in for the current grace period. 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 The qsmaskinit will have one bit for each entity that is
currently expected to check in during each grace period. currently expected to check in during each grace period.
The value of qsmaskinit is assigned to that of qsmask The value of qsmaskinit is assigned to that of qsmask
at the beginning of each grace period. 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 o The characters separated by the ">" indicate the state
of the blocked-tasks lists. A "G" preceding the ">" of the blocked-tasks lists. A "G" preceding the ">"
indicates that at least one task blocked in an RCU indicates that at least one task blocked in an RCU
@ -312,48 +335,39 @@ o Each element of the form "1/1 0:127 ^0" represents one struct
A "." character appears if the corresponding condition A "." character appears if the corresponding condition
does not hold, so that "..>." indicates that no tasks does not hold, so that "..>." indicates that no tasks
are blocked. In contrast, "GE>T" indicates maximal are blocked. In contrast, "GE>T" indicates maximal
inconvenience from blocked tasks. 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 o The numbers separated by the ":" are the range of CPUs
served by this struct rcu_node. This can be helpful served by this struct rcu_node. This can be helpful
in working out how the hierarchy is wired together. in working out how the hierarchy is wired together.
For example, the first entry at the lowest level shows For example, the example rcu_node structure shown above
"0:5", indicating that it covers CPUs 0 through 5. has "0:7", indicating that it covers CPUs 0 through 7.
o The number after the "^" indicates the bit in the o The number after the "^" indicates the bit in the
next higher level rcu_node structure that this next higher level rcu_node structure that this rcu_node
rcu_node structure corresponds to. structure corresponds to. For example, the "d/d ..>. 4:7
^1" has a "1" in this position, indicating that it
For example, the first entry at the lowest level shows corresponds to the "1" bit in the "3" shown in the
"^0", indicating that it corresponds to bit zero in "3/3 ..>. 0:7 ^0" entry on the next level up.
the first entry at the middle level.
The output of "cat rcu/rcu_pending" looks as follows: The output of "cat rcu/rcu_sched/rcu_pending" looks as follows:
rcu_sched: 0!np=26111 qsp=29 rpq=5386 cbr=1 cng=570 gpc=3674 gps=577 nn=15903
0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nn=146741 1!np=28913 qsp=35 rpq=6097 cbr=1 cng=448 gpc=3700 gps=554 nn=18113
1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nn=155792 2!np=32740 qsp=37 rpq=6202 cbr=0 cng=476 gpc=4627 gps=546 nn=20889
2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nn=136629 3 np=23679 qsp=22 rpq=5044 cbr=1 cng=415 gpc=3403 gps=347 nn=14469
3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nn=137723 4!np=30714 qsp=4 rpq=5574 cbr=0 cng=528 gpc=3931 gps=639 nn=20042
4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nn=123110 5 np=28910 qsp=2 rpq=5246 cbr=0 cng=428 gpc=4105 gps=709 nn=18422
5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nn=137456 6!np=38648 qsp=5 rpq=7076 cbr=0 cng=840 gpc=4072 gps=961 nn=25699
6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nn=120834 7 np=37275 qsp=2 rpq=6873 cbr=0 cng=868 gpc=3416 gps=971 nn=25147
7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nn=144888
rcu_bh:
0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nn=145314
1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nn=143180
2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nn=117936
3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nn=134863
4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nn=110671
5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nn=133235
6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nn=110921
7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nn=118542
As always, this is once again split into "rcu_sched" and "rcu_bh" The fields are as follows:
portions, with CONFIG_TREE_PREEMPT_RCU kernels having an additional
"rcu_preempt" section. 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 o "np" is the number of times that __rcu_pending() has been invoked
for the corresponding flavor of RCU. for the corresponding flavor of RCU.
@ -377,38 +391,23 @@ o "gpc" is the number of times that an old grace period had
o "gps" is the number of times that a new grace period had started, o "gps" is the number of times that a new grace period had started,
but this CPU was not yet aware of it. but this CPU was not yet aware of it.
o "nn" is the number of times that this CPU needed nothing. Alert o "nn" is the number of times that this CPU needed nothing.
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: The output of "cat rcu/rcuboost" looks as follows:
0:5 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f 0:3 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
balk: nt=0 egt=989 bt=0 nb=0 ny=0 nos=16 balk: nt=0 egt=4695 bt=0 nb=0 ny=56 nos=0
6:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=2f95 bt=300f 4:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894
balk: nt=0 egt=225 bt=0 nb=0 ny=0 nos=6 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 This information is output only for rcu_preempt. Each two-line entry
corresponds to a leaf rcu_node strcuture. The fields are as follows: 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 o "n:m" is the CPU-number range for the corresponding two-line
entry. In the sample output above, the first entry covers entry. In the sample output above, the first entry covers
CPUs zero through five and the second entry covers CPUs 6 CPUs zero through three and the second entry covers CPUs four
and 7. through seven.
o "tasks=TNEB" gives the state of the various segments of the o "tasks=TNEB" gives the state of the various segments of the
rnp->blocked_tasks list: rnp->blocked_tasks list: