1lcnt(3) Erlang Module Definition lcnt(3)
2
6 lcnt - A runtime system Lock Profiling tool.
7
9 The lcnt module is used to profile the internal ethread locks in the
10 Erlang Runtime System. With lcnt enabled, internal counters in the run‐
11 time system are updated each time a lock is taken. The counters stores
12 information about the number of acquisition tries and the number of
13 collisions that has occurred during the acquisition tries. The counters
14 also record the waiting time a lock has caused for a blocked thread
15 when a collision has occurred.
16 The data produced by the lock counters will give an estimate on how
18 well the runtime system will behave from a parallelizable view point
19 for the scenarios tested. This tool was mainly developed to help Erlang
20 runtime developers iron out potential and generic bottlenecks.
21 Locks in the emulator are named after what type of resource they pro‐
23 tect and where in the emulator they are initialized, those are lock
24 'classes'. Most of those locks are also instantiated several times, and
25 given unique identifiers, to increase locking granularity. Typically an
26 instantiated lock protects a disjunct set of the resource, for example
27 ets tables, processes or ports. In other cases it protects a specific
28 range of a resource, for example pix_lock which protects index to
29 process mappings, and is given a unique number within the class. A
30 unique lock in lcnt is referenced by a name (class) and an identifier:
31 {Name, Id}.
32 Some locks in the system are static and protects global resources, for
34 example bif_timers and the run_queue locks. Other locks are dynamic and
35 not necessarily long lived, for example process locks and ets-table
36 locks. The statistics data from short lived locks can be stored sepa‐
37 rately when the locks are deleted. This behavior is by default turned
38 off to save memory but can be turned on via lcnt:rt_opt({copy_save,
39 true}). The lcnt:apply/1,2,3 functions enables this behavior during
40 profiling.
41
43 start() -> {ok, Pid} | {error, {already_started, Pid}}
44 Types:
46 Pid = pid()
48 Starts the lock profiler server. The server only act as a medium
50 for the user and performs filtering and printing of data col‐
51 lected by lcnt:collect/1.
52 stop() -> ok
54 Stops the lock profiler server.
56 collect() -> ok
58 Same as collect(node()).
60 collect(Node) -> ok
62 Types:
64 Node = node()
66 Collects lock statistics from the runtime system. The function
68 starts a server if it is not already started. It then populates
69 the server with lock statistics. If the server held any lock
70 statistics data before the collect then that data is lost.
71 clear() -> ok
73 Same as clear(node()).
75 clear(Node) -> ok
77 Types:
79 Node = node()
81 Clears the internal lock statistics from the runtime system.
83 This does not clear the data on the server only on runtime sys‐
84 tem. All counters for static locks are zeroed, all dynamic locks
85 currently alive are zeroed and all saved locks now destroyed are
86 removed. It also resets the duration timer.
87 conflicts() -> ok
89 Same as conflicts([]).
91 conflicts([Option]) -> ok
93 Types:
95 Option = {sort, Sort} | {reverse, bool()} | {thresholds,
97 [Thresholds]} | {print, [Print | {Print, integer()}]} |
98 {max_locks, MaxLocks} | {combine, bool()}
99 Sort = name | id | type | tries | colls | ratio | time |
100 entry
101 Thresholds = {tries, integer()} | {colls, integer()} | {time,
102 integer()}
103 Print = name | id | type | entry | tries | colls | ratio |
104 time | duration
105 MaxLocks = integer() | none
106 Prints a list of internal locks and its statistics.
108 For option description, see lcnt:inspect/2.
110 locations() -> ok
112 Same as locations([]).
114 locations([Option]) -> ok
116 Types:
118 Option = {sort, Sort} | {thresholds, [Thresholds]} | {print,
120 [Print | {Print, integer()}]} | {max_locks, MaxLocks} | {com‐
121 bine, bool()}
122 Sort = name | id | type | tries | colls | ratio | time |
123 entry
124 Thresholds = {tries, integer()} | {colls, integer()} | {time,
125 integer()}
126 Print = name | id | type | entry | tries | colls | ratio |
127 time | duration
128 MaxLocks = integer() | none
129 Prints a list of internal lock counters by source code loca‐
131 tions.
132 For option description, see lcnt:inspect/2.
134 inspect(Lock) -> ok
136 Same as inspect(Lock, []).
138 inspect(Lock, [Option]) -> ok
140 Types:
142 Lock = Name | {Name, Id | [Id]}
144 Name = atom() | pid() | port()
145 Id = atom() | integer() | pid() | port()
146 Option = {sort, Sort} | {thresholds, [Thresholds]} | {print,
147 [Print | {Print, integer()}]} | {max_locks, MaxLocks} | {com‐
148 bine, bool()} | {locations, bool()}
149 Sort = name | id | type | tries | colls | ratio | time
150 Thresholds = {tries, integer()} | {colls, integer()} | {time,
151 integer()}
152 Print = name | id | type | entry | tries | colls | ratio |
153 time | duration
154 MaxLocks = integer() | none
155 Prints a list of internal lock counters for a specific lock.
157 Lock Name and Id for ports and processes are interchangeable
159 with the use of lcnt:swap_pid_keys/0 and is the reason why pid()
160 and port() options can be used in both Name and Id space. Both
161 pids and ports are special identifiers with stripped creation
162 and can be recreated with lcnt:pid/2,3 and lcnt:port/1,2.
163 Option description:
165 {combine, bool()}:
167 Combine the statistics from different instances of a lock
168 class.
169 Default: true
170 {locations, bool()}:
172 Print the statistics by source file and line numbers.
173 Default: false
174 {max_locks, MaxLocks}:
176 Maximum number of locks printed or no limit with none.
177 Default: 20
178 {print, PrintOptions}:
180 Printing options:
181 name:
183 Named lock or named set of locks (classes). The same name
184 used for initializing the lock in the VM.
185 id:
187 Internal id for set of locks, not always unique. This
188 could be table name for ets tables (db_tab), port id for
189 ports, integer identifiers for allocators, etc.
190 type:
192 Type of lock: rw_mutex, mutex, spinlock, rw_spinlock or
193 proclock.
194 entry:
196 In combination with {locations, true} this option prints
197 the lock operations source file and line number entry-
198 points along with statistics for each entry.
199 tries:
201 Number of acquisitions of this lock.
202 colls:
204 Number of collisions when a thread tried to acquire this
205 lock. This is when a trylock is EBUSY, a write try on read
206 held rw_lock, a try read on write held rw_lock, a thread
207 tries to lock an already locked lock. (Internal states
208 supervises this).
209 ratio:
211 The ratio between the number of collisions and the number
212 of tries (acquisitions) in percentage.
213 time:
215 Accumulated waiting time for this lock. This could be
216 greater than actual wall clock time, it is accumulated for
217 all threads. Trylock conflicts does not accumulate time.
218 duration:
220 Percentage of accumulated waiting time of wall clock time.
221 This percentage can be higher than 100% since accumulated
222 time is from all threads.
223 Default: [name,id,tries,colls,ratio,time,duration]
224 {reverse, bool()}:
226 Reverses the order of sorting.
227 Default: false
228 {sort, Sort}:
230 Column sorting orders.
231 Default: time
232 {thresholds, Thresholds}:
234 Filtering thresholds. Anything values above the threshold
235 value are passed through.
236 Default: [{tries, 0}, {colls, 0}, {time, 0}]
237 information() -> ok
239 Prints lcnt server state and generic information about collected
241 lock statistics.
242 swap_pid_keys() -> ok
244 Swaps places on Name and Id space for ports and processes.
246 load(Filename) -> ok
248 Types:
250 Filename = filename()
252 Restores previously saved data to the server.
254 save(Filename) -> ok
256 Types:
258 Filename = filename()
260 Saves the collected data to file.
262
264 The following functions are used for convenience.
265
267 apply(Fun) -> term()
268 Types:
270 Fun = fun()
272 Same as apply(Fun, []).
274 apply(Fun, Args) -> term()
276 Types:
278 Fun = fun()
280 Args = [term()]
281 Same as apply(Module, Function, Args).
283 apply(Module, Function, Args) -> term()
285 Types:
287 Module = atom()
289 Function = atom()
290 Args = [term()]
291 Clears the lock counters and then setups the instrumentation to
293 save all destroyed locks. After setup the function is called,
294 passing the elements in Args as arguments. When the function
295 returns the statistics are immediately collected to the server.
296 After the collection the instrumentation is returned to its pre‐
297 vious behavior. The result of the applied function is returned.
298 Warning:
300 This function should only be used for micro-benchmarks; it sets
301 copy_save to true for the duration of the call, which can
302 quickly lead to running out of memory.
303 pid(Id, Serial) -> pid()
306 Same as pid(node(), Id, Serial).
308 pid(Node, Id, Serial) -> pid()
310 Types:
312 Node = node()
314 Id = integer()
315 Serial = integer()
316 Creates a process id with creation 0.
318 port(Id) -> port()
320 Same as port(node(), Id).
322 port(Node, Id) -> port()
324 Types:
326 Node = node()
328 Id = integer()
329 Creates a port id with creation 0.
331
333 The following functions control the behavior of the internal counters.
334
336 rt_collect() -> [lock_counter_data()]
337 Same as rt_collect(node()).
339 rt_collect(Node) -> [lock_counter_data()]
341 Types:
343 Node = node()
345 Returns a list of raw lock counter data.
347 rt_clear() -> ok
349 Same as rt_clear(node()).
351 rt_clear(Node) -> ok
353 Types:
355 Node = node()
357 Clear the internal counters. Same as lcnt:clear(Node).
359 rt_mask() -> [category_atom()]
361 Same as rt_mask(node()).
363 rt_mask(Node) -> [category_atom()]
365 Types:
367 Node = node()
369 Refer to rt_mask/2 for a list of valid categories. All cate‐
371 gories are enabled by default.
372 rt_mask(Categories) -> ok | {error, copy_save_enabled}
374 Types:
376 Categories = [atom()]
378 Same as rt_mask(node(), Categories).
380 rt_mask(Node, Categories) -> ok | {error, copy_save_enabled}
382 Types:
384 Node = node()
386 Categories = [atom()]
387 Sets the lock category mask to the given categories.
389 This will fail if the copy_save option is enabled; see
391 lcnt:rt_opt/2.
392 Valid categories are:
394 * allocator
396 * db (ETS tables)
398 * debug
400 * distribution
402 * generic
404 * io
406 * process
408 * scheduler
410 This list is subject to change at any time, as is the category
412 any given lock may belong to.
413 rt_opt({Type, bool()}) -> bool()
415 Same as rt_opt(node(), {Type, Opt}).
417 rt_opt(Node, {Type, bool()}) -> bool()
419 Types:
421 Node = node()
423 Type = copy_save | process_locks
424 Option description:
426 {copy_save, bool()}:
428 Retains the statistics of destroyed locks.
429 Default: false
430 Warning:
432 This option will use a lot of memory when enabled, which must
433 be reclaimed with lcnt:rt_clear. Note that it makes no dis‐
434 tinction between locks that were destroyed and locks for which
435 counting was disabled, so enabling this option will disable
436 changes to the lock category mask.
437 {process_locks, bool()}:
440 Profile process locks, equal to adding process to the lock
441 category mask; see lcnt:rt_mask/2
442 Default: true
443
445 LCNT User's Guide
446Ericsson AB tools 3.4.4 lcnt(3)