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31 .Nd library for accessing hardware performance monitoring counters
39 provides a programming interface that allows applications to use
40 hardware performance counters to gather performance data about
41 specific processes or for the system as a whole.
42 The library is implemented using the lower-level facilities offered by
47 Performance monitoring counters (PMCs) are represented by the library
48 using a software abstraction.
51 PMCs can have two scopes:
55 These PMCs measure events in a whole-system manner, i.e., independent
56 of the currently executing thread.
57 System scope PMCs are allocated on specific CPUs and do not
59 Non-privileged process are allowed to allocate system scope PMCs if the
62 .Va security.bsd.unprivileged_syspmcs
66 These PMCs only measure hardware events when the processes they are
67 attached to are executing on a CPU.
68 In an SMP system, process scope PMCs migrate between CPUs along with
69 their target processes.
72 Orthogonal to PMC scope, PMCs may be allocated in one of two
76 Counting PMCs measure events according to their scope
78 The application needs to explicitly read these counters
79 to retrieve their value.
81 Sampling PMCs cause the CPU to be periodically interrupted
82 and information about its state of execution to be collected.
83 Sampling PMCs are used to profile specific processes and kernel
84 threads or to profile the system as a whole.
87 The scope and operational mode for a software PMC are specified at
89 An application is allowed to allocate multiple PMCs subject
90 to availability of hardware resources.
92 The library uses human-readable strings to name the event being
94 The syntax used for specifying a hardware event along with additional
95 event specific qualifiers (if any) is described in detail in section
96 .Sx "EVENT SPECIFIERS"
99 PMCs are associated with the process that allocated them and
100 will be automatically reclaimed by the system when the process exits.
101 Additionally, process-scope PMCs have to be attached to one or more
102 target processes before they can perform measurements.
103 A process-scope PMC may be attached to those target processes
104 that its owner process would otherwise be permitted to debug.
105 An owner process may attach PMCs to itself allowing
106 it to measure its own behavior.
107 Additionally, on some machine architectures, such self-attached PMCs
108 may be read cheaply using specialized instructions supported by the
111 Certain kinds of PMCs require that a log file be configured before
116 System scope sampling PMCs.
118 Process scope sampling PMCs.
120 Process scope counting PMCs that have been configured to report PMC
121 readings on process context switches or process exits.
124 Up to one log file may be configured per owner process.
125 Events logged to a log file may be subsequently analyzed using the
129 The CPUs known to the PMC library are named by the
130 .Vt "enum pmc_cputype"
132 Supported CPUs include:
134 .Bl -tag -width "Li PMC_CPU_INTEL_CORE2" -compact
135 .It Li PMC_CPU_AMD_K7
138 .It Li PMC_CPU_AMD_K8
141 .It Li PMC_CPU_INTEL_ATOM
144 CPUs and other CPUs conforming to version 3 of the
146 performance measurement architecture.
147 .It Li PMC_CPU_INTEL_CORE
152 CPUs, and other CPUs conforming to version 1 of the
154 performance measurement architecture.
155 .It Li PMC_CPU_INTEL_CORE2
161 CPUs, and other CPUs conforming to version 2 of the
163 performance measurement architecture.
166 PMC supported by this library are named by the
169 Supported PMC kinds include:
171 .Bl -tag -width "Li PMC_CLASS_IAF" -compact
173 Fixed function hardware counters presents in CPUs conforming to the
175 performance measurement architecture version 2 and later.
177 Programmable hardware counters present in CPUs conforming to the
179 performance measurement architecture version 1 and later.
181 Programmable hardware counters present in
185 Programmable hardware counters present in
189 The timestamp counter on i386 and amd64 architecture CPUs.
190 .It Li PMC_CLASS_SOFT
194 Capabilities of performance monitoring hardware are denoted using
198 Supported capabilities include:
200 .Bl -tag -width "Li PMC_CAP_INTERRUPT" -compact
201 .It Li PMC_CAP_CASCADE
202 The ability to cascade counters.
203 .It Li PMC_CAP_DOMWIDE
204 Separate counters tied to each NUMA domain.
206 The ability to count negated to asserted transitions of the hardware
207 conditions being probed for.
208 .It Li PMC_CAP_INTERRUPT
209 The ability to interrupt the CPU.
210 .It Li PMC_CAP_INVERT
211 The ability to invert the sense of the hardware conditions being
213 .It Li PMC_CAP_PRECISE
214 The ability to perform precise sampling.
215 .It Li PMC_CAP_QUALIFIER
216 The hardware allows monitored to be further qualified in some
217 system dependent way.
219 The ability to read from performance counters.
220 .It Li PMC_CAP_SYSTEM
221 The ability to restrict counting of hardware events to when the CPU is
222 running privileged code.
223 .It Li PMC_CAP_SYSWIDE
224 A single counter aggregating events for the whole system.
225 .It Li PMC_CAP_THRESHOLD
226 The ability to ignore simultaneous hardware events below a
227 programmable threshold.
229 The ability to restrict counting of hardware events to those when the
230 CPU is running unprivileged code.
232 The ability to write to performance counters.
234 .Ss CPU Naming Conventions
235 CPUs are named using small integers from zero up to, but
236 excluding, the value returned by function
238 On platforms supporting sparsely numbered CPUs not all the numbers in
239 this range will denote valid CPUs.
240 Operations on non-existent CPUs will return an error.
241 .Ss Functional Grouping of the API
242 This section contains a brief overview of the available functionality
244 Each function listed here is described further in its own manual page.
247 .Bl -tag -width 6n -compact
248 .It Fn pmc_disable , Fn pmc_enable
249 Administratively disable (enable) specific performance monitoring
251 Counters that are disabled will not be available to applications to
254 .It "Convenience Functions"
255 .Bl -tag -width 6n -compact
256 .It Fn pmc_event_names_of_class
257 Returns a list of event names supported by a given PMC type.
258 .It Fn pmc_name_of_capability
261 flag to a human-readable string.
262 .It Fn pmc_name_of_class
265 constant to a human-readable string.
266 .It Fn pmc_name_of_cputype
267 Return a human-readable name for a CPU type.
268 .It Fn pmc_name_of_disposition
269 Return a human-readable string describing a PMC's disposition.
270 .It Fn pmc_name_of_event
271 Convert a numeric event code to a human-readable string.
272 .It Fn pmc_name_of_mode
275 constant to a human-readable name.
276 .It Fn pmc_name_of_state
277 Return a human-readable string describing a PMC's current state.
279 .It "Library Initialization"
280 .Bl -tag -width 6n -compact
282 Initialize the library.
283 This function must be called before any other library function.
285 .It "Log File Handling"
286 .Bl -tag -width 6n -compact
287 .It Fn pmc_configure_logfile
288 Configure a log file for
290 to write logged events to.
291 .It Fn pmc_flush_logfile
292 Flush all pending log data in
295 .It Fn pmc_close_logfile
296 Flush all pending log data and close
300 Append arbitrary user data to the current log file.
303 .Bl -tag -width 6n -compact
304 .It Fn pmc_allocate , Fn pmc_release
305 Allocate (free) a PMC.
306 .It Fn pmc_attach , Fn pmc_detach
307 Attach (detach) a process scope PMC to a target.
308 .It Fn pmc_read , Fn pmc_write , Fn pmc_rw
309 Read (write) a value from (to) a PMC.
310 .It Fn pmc_start , Fn pmc_stop
311 Start (stop) a software PMC.
313 Set the reload value for a sampling PMC.
316 .Bl -tag -width 6n -compact
317 .It Fn pmc_capabilities
318 Retrieve the capabilities for a given PMC.
320 Retrieve information about the CPUs and PMC hardware present in the
322 .It Fn pmc_get_driver_stats
323 Retrieve statistics maintained by
326 Determine the greatest possible CPU number on the system.
328 Return the number of hardware PMCs present in a given CPU.
330 Return information about the state of a given CPU's PMCs.
332 Determine the width of a hardware counter in bits.
334 .It "x86 Architecture Specific API"
335 .Bl -tag -width 6n -compact
337 Returns the processor model specific register number
340 Applications may then use the x86
342 instruction to directly read the contents of the PMC.
345 .Ss Signal Handling Requirements
346 Applications using PMCs are required to handle the following signals:
347 .Bl -tag -width ".Dv SIGBUS"
351 module is unloaded using
353 processes that have PMCs allocated to them will be sent a
359 driver will send a PMC owning process a
364 If any process-mode PMC allocated by it loses all its
367 If the driver encounters an error when writing log data to a
369 This error may be retrieved by a subsequent call to
370 .Fn pmc_flush_logfile .
373 .Ss Typical Program Flow
376 An application would first invoke function
378 to allow the library to initialize itself.
380 Signal handling would then be set up.
382 Next the application would allocate the PMCs it desires using function
385 Initial values for PMCs may be set using function
388 If a log file is necessary for the PMCs to work, it would
389 be configured using function
390 .Fn pmc_configure_logfile .
392 Process scope PMCs would then be attached to their target processes
396 The PMCs would then be started using function
399 Once started, the values of counting PMCs may be read using function
401 For PMCs that write events to the log file, this logged data would be
402 read and parsed using the
406 PMCs are stopped using function
408 and process scope PMCs are detached from their targets using
412 Before the process exits, its may release its PMCs using function
414 Any configured log file may be closed using function
415 .Fn pmc_configure_logfile .
418 Event specifiers are strings comprising of an event name, followed by
419 optional parameters modifying the semantics of the hardware event
421 Event names are PMC architecture dependent, but the PMC library defines
422 machine independent aliases for commonly used events.
424 Event specifiers spellings are case-insensitive and space characters,
425 periods, underscores and hyphens are considered equivalent to each other.
426 Thus the event specifiers
427 .Qq "Example Event" ,
428 .Qq "example-event" ,
432 .Ss PMC Architecture Dependent Events
433 PMC architecture dependent event specifiers are described in the
434 following manual pages:
435 .Bl -column " PMC_CLASS_TSC " "MANUAL PAGE "
436 .It Em "PMC Class" Ta Em "Manual Page"
437 .It Li PMC_CLASS_IAF Ta Xr pmc.iaf 3
438 .It Li PMC_CLASS_IAP Ta Xr pmc.atom 3 , Xr pmc.core 3 , Xr pmc.core2 3
439 .It Li PMC_CLASS_K7 Ta Xr pmc.k7 3
440 .It Li PMC_CLASS_K8 Ta Xr pmc.k8 3
441 .It Li PMC_CLASS_TSC Ta Xr pmc.tsc 3
443 .Ss Event Name Aliases
444 Event name aliases are PMC-independent names for commonly used events.
445 The following aliases are known to this version of the
448 .Bl -tag -width indent
450 Measure the number of branches retired.
451 .It Li branch-mispredicts
452 Measure the number of retired branches that were mispredicted.
454 Measure processor cycles.
455 This event is implemented using the processor's Time Stamp Counter
458 Measure the number of data cache misses.
460 Measure the number of instruction cache misses.
462 Measure the number of instructions retired.
464 Measure the number of interrupts seen.
465 .It Li unhalted-cycles
466 Measure the number of cycles the processor is not in a halted
470 The interface between the
474 driver is intended to be private to the implementation and may
476 In order to ease forward compatibility with future versions of the
478 driver, applications are urged to dynamically link with the
491 .Xr pmc.haswelluc 3 ,
492 .Xr pmc.haswellxeon 3 ,
494 .Xr pmc.ivybridge 3 ,
495 .Xr pmc.ivybridgexeon 3 ,
498 .Xr pmc.sandybridge 3 ,
499 .Xr pmc.sandybridgeuc 3 ,
500 .Xr pmc.sandybridgexeon 3 ,
504 .Xr pmc.westmereuc 3 ,
507 .Xr pmc_capabilities 3 ,
508 .Xr pmc_configure_logfile 3 ,
510 .Xr pmc_event_names_of_class 3 ,
511 .Xr pmc_get_driver_stats 3 ,
514 .Xr pmc_name_of_capability 3 ,
525 library first appeared in
530 library was written by
531 .An Joseph Koshy Aq Mt jkoshy@FreeBSD.org .