diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.html | 2 | ||||
| -rw-r--r-- | Documentation/RCU/trace.txt | 535 |
3 files changed, 1 insertions, 538 deletions
diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX index 1672573b037a..f46980c060aa 100644 --- a/Documentation/RCU/00-INDEX +++ b/Documentation/RCU/00-INDEX @@ -28,8 +28,6 @@ stallwarn.txt - RCU CPU stall warnings (module parameter rcu_cpu_stall_suppress) torture.txt - RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST) -trace.txt - - CONFIG_RCU_TRACE debugfs files and formats UP.txt - RCU on Uniprocessor Systems whatisRCU.txt diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 0e6550a8c926..95b30fa25d56 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -2034,7 +2034,7 @@ guard against mishaps and misuse: some other synchronization mechanism, for example, reference counting. <li> In kernels built with <tt>CONFIG_RCU_TRACE=y</tt>, RCU-related - information is provided via both debugfs and event tracing. + information is provided via event tracing. <li> Open-coded use of <tt>rcu_assign_pointer()</tt> and <tt>rcu_dereference()</tt> to create typical linked data structures can be surprisingly error-prone. diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt deleted file mode 100644 index 6549012033f9..000000000000 --- a/Documentation/RCU/trace.txt +++ /dev/null @@ -1,535 +0,0 @@ -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_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_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 cnq=1/0:1 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 cnq=1/0:0 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 cnq=1/1:1 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 cnq=1/1:0 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 cnq=1/0:1 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 cnq=1/0:1 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 cnq=1/0:1 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 cnq=1/0:0 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 cnq=1/0:1 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 cnq=1/0:0 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 cnq=1/0:0 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 cnq=1/0:0 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 cnq=1/0:1 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 cnq=1/0:0 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 cnq=1/0:0 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 cnq=1/0:1 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 wd1=0 wd2=0 wd3=5 enq=0 sc=21872 - -These fields are as follows: - -o "s" is the sequence number, with an odd number indicating that - an expedited grace period is in progress. - -o "wd1", "wd2", and "wd3" 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 "enq" is the number of quiescent states still outstanding. - -o "sc" is the number of times that the attempt to start a - new expedited grace period succeeded. - - -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. |