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1 | CONFIG_RCU_TRACE debugfs Files and Formats |
2 | ||
3 | ||
8e79e1f9 PM |
4 | The rcutree and rcutiny implementations of RCU provide debugfs trace |
5 | output that summarizes counters and state. This information is useful for | |
6 | debugging RCU itself, and can sometimes also help to debug abuses of RCU. | |
7 | The following sections describe the debugfs files and formats, first | |
8 | for rcutree and next for rcutiny. | |
64db4cff PM |
9 | |
10 | ||
8e79e1f9 | 11 | CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats |
64db4cff | 12 | |
40e80c46 | 13 | These implementations of RCU provide several debugfs directories under the |
90e6ac36 PM |
14 | top-level directory "rcu": |
15 | ||
40e80c46 PM |
16 | rcu/rcu_bh |
17 | rcu/rcu_preempt | |
18 | rcu/rcu_sched | |
19 | ||
20 | Each directory contains files for the corresponding flavor of RCU. | |
21 | Note that rcu/rcu_preempt is only present for CONFIG_TREE_PREEMPT_RCU. | |
22 | For CONFIG_TREE_RCU, the RCU flavor maps onto the RCU-sched flavor, | |
23 | so that activity for both appears in rcu/rcu_sched. | |
24 | ||
25 | In addition, the following file appears in the top-level directory: | |
26 | rcu/rcutorture. This file displays rcutorture test progress. The output | |
27 | of "cat rcu/rcutorture" looks as follows: | |
28 | ||
29 | rcutorture test sequence: 0 (test in progress) | |
30 | rcutorture update version number: 615 | |
31 | ||
32 | The first line shows the number of rcutorture tests that have completed | |
33 | since boot. If a test is currently running, the "(test in progress)" | |
34 | string will appear as shown above. The second line shows the number of | |
35 | update cycles that the current test has started, or zero if there is | |
36 | no test in progress. | |
37 | ||
38 | ||
39 | Within each flavor directory (rcu/rcu_bh, rcu/rcu_sched, and possibly | |
40 | also rcu/rcu_preempt) the following files will be present: | |
41 | ||
42 | rcudata: | |
90e6ac36 | 43 | Displays fields in struct rcu_data. |
d484a215 PM |
44 | rcuexp: |
45 | Displays statistics for expedited grace periods. | |
40e80c46 | 46 | rcugp: |
90e6ac36 | 47 | Displays grace-period counters. |
40e80c46 | 48 | rcuhier: |
90e6ac36 | 49 | Displays the struct rcu_node hierarchy. |
40e80c46 | 50 | rcu_pending: |
90e6ac36 PM |
51 | Displays counts of the reasons rcu_pending() decided that RCU had |
52 | work to do. | |
40e80c46 | 53 | rcuboost: |
90e6ac36 PM |
54 | Displays RCU boosting statistics. Only present if |
55 | CONFIG_RCU_BOOST=y. | |
64db4cff | 56 | |
40e80c46 PM |
57 | The output of "cat rcu/rcu_preempt/rcudata" looks as follows: |
58 | ||
59 | 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 | |
60 | 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 | |
61 | 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 | |
62 | 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 | |
63 | 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 | |
64 | 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 | |
65 | 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 | |
66 | 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 | |
67 | ||
68 | This file has one line per CPU, or eight for this 8-CPU system. | |
69 | The fields are as follows: | |
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70 | |
71 | o The number at the beginning of each line is the CPU number. | |
72 | CPUs numbers followed by an exclamation mark are offline, | |
73 | but have been online at least once since boot. There will be | |
74 | no output for CPUs that have never been online, which can be | |
75 | a good thing in the surprisingly common case where NR_CPUS is | |
76 | substantially larger than the number of actual CPUs. | |
77 | ||
78 | o "c" is the count of grace periods that this CPU believes have | |
40e80c46 PM |
79 | completed. Offlined CPUs and CPUs in dynticks idle mode may lag |
80 | quite a ways behind, for example, CPU 4 under "rcu_sched" above, | |
81 | which has been offline through 16 RCU grace periods. It is not | |
82 | unusual to see offline CPUs lagging by thousands of grace periods. | |
83 | Note that although the grace-period number is an unsigned long, | |
84 | it is printed out as a signed long to allow more human-friendly | |
85 | representation near boot time. | |
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86 | |
87 | o "g" is the count of grace periods that this CPU believes have | |
2fa218d8 PM |
88 | started. Again, offlined CPUs and CPUs in dynticks idle mode |
89 | may lag behind. If the "c" and "g" values are equal, this CPU | |
90 | has already reported a quiescent state for the last RCU grace | |
91 | period that it is aware of, otherwise, the CPU believes that it | |
92 | owes RCU a quiescent state. | |
64db4cff PM |
93 | |
94 | o "pq" indicates that this CPU has passed through a quiescent state | |
95 | for the current grace period. It is possible for "pq" to be | |
96 | "1" and "c" different than "g", which indicates that although | |
97 | the CPU has passed through a quiescent state, either (1) this | |
98 | CPU has not yet reported that fact, (2) some other CPU has not | |
99 | yet reported for this grace period, or (3) both. | |
100 | ||
64db4cff | 101 | o "qp" indicates that RCU still expects a quiescent state from |
2fa218d8 PM |
102 | this CPU. Offlined CPUs and CPUs in dyntick idle mode might |
103 | well have qp=1, which is OK: RCU is still ignoring them. | |
64db4cff | 104 | |
64db4cff | 105 | o "dt" is the current value of the dyntick counter that is incremented |
40e80c46 PM |
106 | when entering or leaving idle, either due to a context switch or |
107 | due to an interrupt. This number is even if the CPU is in idle | |
108 | from RCU's viewpoint and odd otherwise. The number after the | |
109 | first "/" is the interrupt nesting depth when in idle state, | |
110 | or a large number added to the interrupt-nesting depth when | |
111 | running a non-idle task. Some architectures do not accurately | |
112 | count interrupt nesting when running in non-idle kernel context, | |
113 | which can result in interesting anomalies such as negative | |
114 | interrupt-nesting levels. The number after the second "/" | |
115 | is the NMI nesting depth. | |
64db4cff | 116 | |
64db4cff PM |
117 | o "df" is the number of times that some other CPU has forced a |
118 | quiescent state on behalf of this CPU due to this CPU being in | |
40e80c46 | 119 | idle state. |
64db4cff | 120 | |
64db4cff PM |
121 | o "of" is the number of times that some other CPU has forced a |
122 | quiescent state on behalf of this CPU due to this CPU being | |
2fa218d8 | 123 | offline. In a perfect world, this might never happen, but it |
64db4cff PM |
124 | turns out that offlining and onlining a CPU can take several grace |
125 | periods, and so there is likely to be an extended period of time | |
126 | when RCU believes that the CPU is online when it really is not. | |
127 | Please note that erring in the other direction (RCU believing a | |
128 | CPU is offline when it is really alive and kicking) is a fatal | |
129 | error, so it makes sense to err conservatively. | |
130 | ||
64db4cff | 131 | o "ql" is the number of RCU callbacks currently residing on |
40e80c46 PM |
132 | this CPU. The first number is the number of "lazy" callbacks |
133 | that are known to RCU to only be freeing memory, and the number | |
134 | after the "/" is the total number of callbacks, lazy or not. | |
135 | These counters count callbacks regardless of what phase of | |
136 | grace-period processing that they are in (new, waiting for | |
137 | grace period to start, waiting for grace period to end, ready | |
138 | to invoke). | |
64db4cff | 139 | |
0ac3d136 PM |
140 | o "qs" gives an indication of the state of the callback queue |
141 | with four characters: | |
142 | ||
143 | "N" Indicates that there are callbacks queued that are not | |
144 | ready to be handled by the next grace period, and thus | |
145 | will be handled by the grace period following the next | |
146 | one. | |
147 | ||
148 | "R" Indicates that there are callbacks queued that are | |
149 | ready to be handled by the next grace period. | |
150 | ||
151 | "W" Indicates that there are callbacks queued that are | |
152 | waiting on the current grace period. | |
153 | ||
154 | "D" Indicates that there are callbacks queued that have | |
155 | already been handled by a prior grace period, and are | |
156 | thus waiting to be invoked. Note that callbacks in | |
157 | the process of being invoked are not counted here. | |
158 | Callbacks in the process of being invoked are those | |
159 | that have been removed from the rcu_data structures | |
160 | queues by rcu_do_batch(), but which have not yet been | |
161 | invoked. | |
162 | ||
163 | If there are no callbacks in a given one of the above states, | |
164 | the corresponding character is replaced by ".". | |
165 | ||
40e80c46 PM |
166 | o "b" is the batch limit for this CPU. If more than this number |
167 | of RCU callbacks is ready to invoke, then the remainder will | |
168 | be deferred. | |
169 | ||
170 | o "ci" is the number of RCU callbacks that have been invoked for | |
171 | this CPU. Note that ci+nci+ql is the number of callbacks that have | |
172 | been registered in absence of CPU-hotplug activity. | |
173 | ||
174 | o "nci" is the number of RCU callbacks that have been offloaded from | |
175 | this CPU. This will always be zero unless the kernel was built | |
176 | with CONFIG_RCU_NOCB_CPU=y and the "rcu_nocbs=" kernel boot | |
177 | parameter was specified. | |
178 | ||
179 | o "co" is the number of RCU callbacks that have been orphaned due to | |
180 | this CPU going offline. These orphaned callbacks have been moved | |
181 | to an arbitrarily chosen online CPU. | |
182 | ||
183 | o "ca" is the number of RCU callbacks that have been adopted by this | |
184 | CPU due to other CPUs going offline. Note that ci+co-ca+ql is | |
185 | the number of RCU callbacks registered on this CPU. | |
186 | ||
187 | ||
188 | Kernels compiled with CONFIG_RCU_BOOST=y display the following from | |
189 | /debug/rcu/rcu_preempt/rcudata: | |
190 | ||
191 | 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 | |
192 | 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 | |
193 | 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 | |
194 | 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 | |
195 | 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 | |
196 | 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 | |
197 | 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 | |
198 | 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 | |
199 | ||
200 | This is similar to the output discussed above, but contains the following | |
201 | additional fields: | |
202 | ||
90e6ac36 | 203 | o "kt" is the per-CPU kernel-thread state. The digit preceding |
15ba0ba8 | 204 | the first slash is zero if there is no work pending and 1 |
5ece5bab PM |
205 | otherwise. The character between the first pair of slashes is |
206 | as follows: | |
90e6ac36 PM |
207 | |
208 | "S" The kernel thread is stopped, in other words, all | |
209 | CPUs corresponding to this rcu_node structure are | |
210 | offline. | |
211 | ||
212 | "R" The kernel thread is running. | |
213 | ||
214 | "W" The kernel thread is waiting because there is no work | |
215 | for it to do. | |
216 | ||
15ba0ba8 PM |
217 | "O" The kernel thread is waiting because it has been |
218 | forced off of its designated CPU or because its | |
219 | ->cpus_allowed mask permits it to run on other than | |
220 | its designated CPU. | |
221 | ||
90e6ac36 PM |
222 | "Y" The kernel thread is yielding to avoid hogging CPU. |
223 | ||
224 | "?" Unknown value, indicates a bug. | |
225 | ||
15ba0ba8 PM |
226 | The number after the final slash is the CPU that the kthread |
227 | is actually running on. | |
228 | ||
d5988af5 PM |
229 | This field is displayed only for CONFIG_RCU_BOOST kernels. |
230 | ||
5ece5bab PM |
231 | o "ktl" is the low-order 16 bits (in hexadecimal) of the count of |
232 | the number of times that this CPU's per-CPU kthread has gone | |
233 | through its loop servicing invoke_rcu_cpu_kthread() requests. | |
234 | ||
d5988af5 PM |
235 | This field is displayed only for CONFIG_RCU_BOOST kernels. |
236 | ||
269dcc1c | 237 | |
d484a215 PM |
238 | The output of "cat rcu/rcu_preempt/rcuexp" looks as follows: |
239 | ||
240 | s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872 | |
241 | ||
242 | These fields are as follows: | |
243 | ||
244 | o "s" is the starting sequence number. | |
245 | ||
246 | o "d" is the ending sequence number. When the starting and ending | |
247 | numbers differ, there is an expedited grace period in progress. | |
248 | ||
249 | o "w" is the number of times that the sequence numbers have been | |
250 | in danger of wrapping. | |
251 | ||
252 | o "tf" is the number of times that contention has resulted in a | |
253 | failure to begin an expedited grace period. | |
254 | ||
255 | o "wd1" and "wd2" are the number of times that an attempt to | |
256 | start an expedited grace period found that someone else had | |
257 | completed an expedited grace period that satisfies the | |
258 | attempted request. "Our work is done." | |
259 | ||
260 | o "n" is number of times that contention was so great that | |
261 | the request was demoted from an expedited grace period to | |
262 | a normal grace period. | |
263 | ||
264 | o "sc" is the number of times that the attempt to start a | |
265 | new expedited grace period succeeded. | |
266 | ||
267 | o "dt" is the number of times that we attempted to update | |
268 | the "d" counter. | |
269 | ||
270 | o "dl" is the number of times that we failed to update the "d" | |
271 | counter. | |
272 | ||
273 | o "dx" is the number of times that we succeeded in updating | |
274 | the "d" counter. | |
275 | ||
276 | ||
40e80c46 | 277 | The output of "cat rcu/rcu_preempt/rcugp" looks as follows: |
6fd9b3a4 | 278 | |
40e80c46 | 279 | completed=31249 gpnum=31250 age=1 max=18 |
64db4cff | 280 | |
40e80c46 | 281 | These fields are taken from the rcu_state structure, and are as follows: |
64db4cff PM |
282 | |
283 | o "completed" is the number of grace periods that have completed. | |
284 | It is comparable to the "c" field from rcu/rcudata in that a | |
285 | CPU whose "c" field matches the value of "completed" is aware | |
286 | that the corresponding RCU grace period has completed. | |
287 | ||
288 | o "gpnum" is the number of grace periods that have started. It is | |
40e80c46 PM |
289 | similarly comparable to the "g" field from rcu/rcudata in that |
290 | a CPU whose "g" field matches the value of "gpnum" is aware that | |
291 | the corresponding RCU grace period has started. | |
64db4cff | 292 | |
40e80c46 PM |
293 | If these two fields are equal, then there is no grace period |
294 | in progress, in other words, RCU is idle. On the other hand, | |
295 | if the two fields differ (as they are above), then an RCU grace | |
296 | period is in progress. | |
64db4cff | 297 | |
40e80c46 PM |
298 | o "age" is the number of jiffies that the current grace period |
299 | has extended for, or zero if there is no grace period currently | |
300 | in effect. | |
64db4cff | 301 | |
40e80c46 PM |
302 | o "max" is the age in jiffies of the longest-duration grace period |
303 | thus far. | |
64db4cff | 304 | |
40e80c46 | 305 | The output of "cat rcu/rcu_preempt/rcuhier" looks as follows: |
64db4cff | 306 | |
40e80c46 PM |
307 | c=14407 g=14408 s=0 jfq=2 j=c863 nfqs=12040/nfqsng=0(12040) fqlh=1051 oqlen=0/0 |
308 | 3/3 ..>. 0:7 ^0 | |
309 | e/e ..>. 0:3 ^0 d/d ..>. 4:7 ^1 | |
64db4cff | 310 | |
40e80c46 | 311 | The fields are as follows: |
64db4cff | 312 | |
40e80c46 | 313 | o "c" is exactly the same as "completed" under rcu/rcu_preempt/rcugp. |
64db4cff | 314 | |
40e80c46 PM |
315 | o "g" is exactly the same as "gpnum" under rcu/rcu_preempt/rcugp. |
316 | ||
317 | o "s" is the current state of the force_quiescent_state() | |
64db4cff PM |
318 | state machine. |
319 | ||
320 | o "jfq" is the number of jiffies remaining for this grace period | |
321 | before force_quiescent_state() is invoked to help push things | |
40e80c46 PM |
322 | along. Note that CPUs in idle mode throughout the grace period |
323 | will not report on their own, but rather must be check by some | |
324 | other CPU via force_quiescent_state(). | |
64db4cff PM |
325 | |
326 | o "j" is the low-order four hex digits of the jiffies counter. | |
327 | Yes, Paul did run into a number of problems that turned out to | |
328 | be due to the jiffies counter no longer counting. Why do you ask? | |
329 | ||
330 | o "nfqs" is the number of calls to force_quiescent_state() since | |
331 | boot. | |
332 | ||
333 | o "nfqsng" is the number of useless calls to force_quiescent_state(), | |
334 | where there wasn't actually a grace period active. This can | |
40e80c46 PM |
335 | no longer happen due to grace-period processing being pushed |
336 | into a kthread. The number in parentheses is the difference | |
64db4cff PM |
337 | between "nfqs" and "nfqsng", or the number of times that |
338 | force_quiescent_state() actually did some real work. | |
339 | ||
340 | o "fqlh" is the number of calls to force_quiescent_state() that | |
341 | exited immediately (without even being counted in nfqs above) | |
342 | due to contention on ->fqslock. | |
343 | ||
40e80c46 PM |
344 | o Each element of the form "3/3 ..>. 0:7 ^0" represents one rcu_node |
345 | structure. Each line represents one level of the hierarchy, | |
346 | from root to leaves. It is best to think of the rcu_data | |
347 | structures as forming yet another level after the leaves. | |
348 | Note that there might be either one, two, three, or even four | |
349 | levels of rcu_node structures, depending on the relationship | |
350 | between CONFIG_RCU_FANOUT, CONFIG_RCU_FANOUT_LEAF (possibly | |
351 | adjusted using the rcu_fanout_leaf kernel boot parameter), and | |
352 | CONFIG_NR_CPUS (possibly adjusted using the nr_cpu_ids count of | |
353 | possible CPUs for the booting hardware). | |
0edf1a68 | 354 | |
64db4cff PM |
355 | o The numbers separated by the "/" are the qsmask followed |
356 | by the qsmaskinit. The qsmask will have one bit | |
40e80c46 PM |
357 | set for each entity in the next lower level that has |
358 | not yet checked in for the current grace period ("e" | |
359 | indicating CPUs 5, 6, and 7 in the example above). | |
64db4cff PM |
360 | The qsmaskinit will have one bit for each entity that is |
361 | currently expected to check in during each grace period. | |
362 | The value of qsmaskinit is assigned to that of qsmask | |
363 | at the beginning of each grace period. | |
364 | ||
0edf1a68 | 365 | o The characters separated by the ">" indicate the state |
12f5f524 | 366 | of the blocked-tasks lists. A "G" preceding the ">" |
0edf1a68 PM |
367 | indicates that at least one task blocked in an RCU |
368 | read-side critical section blocks the current grace | |
12f5f524 PM |
369 | period, while a "E" preceding the ">" indicates that |
370 | at least one task blocked in an RCU read-side critical | |
371 | section blocks the current expedited grace period. | |
372 | A "T" character following the ">" indicates that at | |
373 | least one task is blocked within an RCU read-side | |
374 | critical section, regardless of whether any current | |
375 | grace period (expedited or normal) is inconvenienced. | |
376 | A "." character appears if the corresponding condition | |
377 | does not hold, so that "..>." indicates that no tasks | |
378 | are blocked. In contrast, "GE>T" indicates maximal | |
40e80c46 PM |
379 | inconvenience from blocked tasks. CONFIG_TREE_RCU |
380 | builds of the kernel will always show "..>.". | |
0edf1a68 | 381 | |
64db4cff PM |
382 | o The numbers separated by the ":" are the range of CPUs |
383 | served by this struct rcu_node. This can be helpful | |
384 | in working out how the hierarchy is wired together. | |
385 | ||
40e80c46 PM |
386 | For example, the example rcu_node structure shown above |
387 | has "0:7", indicating that it covers CPUs 0 through 7. | |
64db4cff PM |
388 | |
389 | o The number after the "^" indicates the bit in the | |
40e80c46 PM |
390 | next higher level rcu_node structure that this rcu_node |
391 | structure corresponds to. For example, the "d/d ..>. 4:7 | |
392 | ^1" has a "1" in this position, indicating that it | |
393 | corresponds to the "1" bit in the "3" shown in the | |
394 | "3/3 ..>. 0:7 ^0" entry on the next level up. | |
395 | ||
396 | ||
397 | The output of "cat rcu/rcu_sched/rcu_pending" looks as follows: | |
398 | ||
399 | 0!np=26111 qsp=29 rpq=5386 cbr=1 cng=570 gpc=3674 gps=577 nn=15903 | |
400 | 1!np=28913 qsp=35 rpq=6097 cbr=1 cng=448 gpc=3700 gps=554 nn=18113 | |
401 | 2!np=32740 qsp=37 rpq=6202 cbr=0 cng=476 gpc=4627 gps=546 nn=20889 | |
402 | 3 np=23679 qsp=22 rpq=5044 cbr=1 cng=415 gpc=3403 gps=347 nn=14469 | |
403 | 4!np=30714 qsp=4 rpq=5574 cbr=0 cng=528 gpc=3931 gps=639 nn=20042 | |
404 | 5 np=28910 qsp=2 rpq=5246 cbr=0 cng=428 gpc=4105 gps=709 nn=18422 | |
405 | 6!np=38648 qsp=5 rpq=7076 cbr=0 cng=840 gpc=4072 gps=961 nn=25699 | |
406 | 7 np=37275 qsp=2 rpq=6873 cbr=0 cng=868 gpc=3416 gps=971 nn=25147 | |
407 | ||
408 | The fields are as follows: | |
409 | ||
410 | o The leading number is the CPU number, with "!" indicating | |
411 | an offline CPU. | |
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412 | |
413 | o "np" is the number of times that __rcu_pending() has been invoked | |
414 | for the corresponding flavor of RCU. | |
415 | ||
416 | o "qsp" is the number of times that the RCU was waiting for a | |
417 | quiescent state from this CPU. | |
418 | ||
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419 | o "rpq" is the number of times that the CPU had passed through |
420 | a quiescent state, but not yet reported it to RCU. | |
421 | ||
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422 | o "cbr" is the number of times that this CPU had RCU callbacks |
423 | that had passed through a grace period, and were thus ready | |
424 | to be invoked. | |
425 | ||
426 | o "cng" is the number of times that this CPU needed another | |
427 | grace period while RCU was idle. | |
428 | ||
429 | o "gpc" is the number of times that an old grace period had | |
430 | completed, but this CPU was not yet aware of it. | |
431 | ||
432 | o "gps" is the number of times that a new grace period had started, | |
433 | but this CPU was not yet aware of it. | |
434 | ||
40e80c46 | 435 | o "nn" is the number of times that this CPU needed nothing. |
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436 | |
437 | ||
438 | The output of "cat rcu/rcuboost" looks as follows: | |
439 | ||
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440 | 0:3 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894 |
441 | balk: nt=0 egt=4695 bt=0 nb=0 ny=56 nos=0 | |
442 | 4:7 tasks=.... kt=W ntb=0 neb=0 nnb=0 j=c864 bt=c894 | |
443 | balk: nt=0 egt=6541 bt=0 nb=0 ny=126 nos=0 | |
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444 | |
445 | This information is output only for rcu_preempt. Each two-line entry | |
446 | corresponds to a leaf rcu_node strcuture. The fields are as follows: | |
447 | ||
448 | o "n:m" is the CPU-number range for the corresponding two-line | |
449 | entry. In the sample output above, the first entry covers | |
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450 | CPUs zero through three and the second entry covers CPUs four |
451 | through seven. | |
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452 | |
453 | o "tasks=TNEB" gives the state of the various segments of the | |
454 | rnp->blocked_tasks list: | |
455 | ||
456 | "T" This indicates that there are some tasks that blocked | |
457 | while running on one of the corresponding CPUs while | |
458 | in an RCU read-side critical section. | |
459 | ||
460 | "N" This indicates that some of the blocked tasks are preventing | |
461 | the current normal (non-expedited) grace period from | |
462 | completing. | |
463 | ||
464 | "E" This indicates that some of the blocked tasks are preventing | |
465 | the current expedited grace period from completing. | |
466 | ||
467 | "B" This indicates that some of the blocked tasks are in | |
468 | need of RCU priority boosting. | |
469 | ||
470 | Each character is replaced with "." if the corresponding | |
471 | condition does not hold. | |
472 | ||
473 | o "kt" is the state of the RCU priority-boosting kernel | |
474 | thread associated with the corresponding rcu_node structure. | |
475 | The state can be one of the following: | |
476 | ||
477 | "S" The kernel thread is stopped, in other words, all | |
478 | CPUs corresponding to this rcu_node structure are | |
479 | offline. | |
480 | ||
481 | "R" The kernel thread is running. | |
482 | ||
483 | "W" The kernel thread is waiting because there is no work | |
484 | for it to do. | |
485 | ||
486 | "Y" The kernel thread is yielding to avoid hogging CPU. | |
487 | ||
488 | "?" Unknown value, indicates a bug. | |
489 | ||
490 | o "ntb" is the number of tasks boosted. | |
491 | ||
492 | o "neb" is the number of tasks boosted in order to complete an | |
493 | expedited grace period. | |
494 | ||
495 | o "nnb" is the number of tasks boosted in order to complete a | |
496 | normal (non-expedited) grace period. When boosting a task | |
497 | that was blocking both an expedited and a normal grace period, | |
498 | it is counted against the expedited total above. | |
499 | ||
500 | o "j" is the low-order 16 bits of the jiffies counter in | |
501 | hexadecimal. | |
502 | ||
503 | o "bt" is the low-order 16 bits of the value that the jiffies | |
504 | counter will have when we next start boosting, assuming that | |
505 | the current grace period does not end beforehand. This is | |
506 | also in hexadecimal. | |
507 | ||
508 | o "balk: nt" counts the number of times we didn't boost (in | |
509 | other words, we balked) even though it was time to boost because | |
510 | there were no blocked tasks to boost. This situation occurs | |
511 | when there is one blocked task on one rcu_node structure and | |
512 | none on some other rcu_node structure. | |
513 | ||
514 | o "egt" counts the number of times we balked because although | |
515 | there were blocked tasks, none of them were blocking the | |
516 | current grace period, whether expedited or otherwise. | |
517 | ||
518 | o "bt" counts the number of times we balked because boosting | |
519 | had already been initiated for the current grace period. | |
520 | ||
521 | o "nb" counts the number of times we balked because there | |
522 | was at least one task blocking the current non-expedited grace | |
523 | period that never had blocked. If it is already running, it | |
524 | just won't help to boost its priority! | |
525 | ||
526 | o "ny" counts the number of times we balked because it was | |
527 | not yet time to start boosting. | |
528 | ||
529 | o "nos" counts the number of times we balked for other | |
530 | reasons, e.g., the grace period ended first. | |
531 | ||
532 | ||
7807acdb | 533 | CONFIG_TINY_RCU debugfs Files and Formats |
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534 | |
535 | These implementations of RCU provides a single debugfs file under the | |
536 | top-level directory RCU, namely rcu/rcudata, which displays fields in | |
7807acdb | 537 | rcu_bh_ctrlblk and rcu_sched_ctrlblk. |
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538 | |
539 | The output of "cat rcu/rcudata" is as follows: | |
540 | ||
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541 | rcu_sched: qlen: 0 |
542 | rcu_bh: qlen: 0 | |
543 | ||
7807acdb PM |
544 | This is split into rcu_sched and rcu_bh sections. The field is as |
545 | follows: | |
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546 | |
547 | o "qlen" is the number of RCU callbacks currently waiting either | |
548 | for an RCU grace period or waiting to be invoked. This is the | |
549 | only field present for rcu_sched and rcu_bh, due to the | |
550 | short-circuiting of grace period in those two cases. |