xref: /freebsd/lib/libpmc/pmc.3 (revision 0782240958117692ab9861abb5483c9e64f6bc39)
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24.\" $FreeBSD$
25.\"
26.Dd November 24, 2008
27.Dt PMC 3
28.Os
29.Sh NAME
30.Nm pmc
31.Nd library for accessing hardware performance monitoring counters
32.Sh LIBRARY
33.Lb libpmc
34.Sh SYNOPSIS
35.In pmc.h
36.Sh DESCRIPTION
37The
38.Lb libpmc
39provides a programming interface that allows applications to use
40hardware performance counters to gather performance data about
41specific processes or for the system as a whole.
42The library is implemented using the lower-level facilities offered by
43the
44.Xr hwpmc 4
45driver.
46.Ss Key Concepts
47Performance monitoring counters (PMCs) are represented by the library
48using a software abstraction.
49These
50.Dq abstract
51PMCs can have two scopes:
52.Bl -bullet
53.It
54System scope.
55These PMCs measure events in a whole-system manner, i.e., independent
56of the currently executing thread.
57System scope PMCs are allocated on specific CPUs and do not
58migrate between CPUs.
59Non-privileged process are allowed to allocate system scope PMCs if the
60.Xr hwpmc 4
61sysctl tunable:
62.Va security.bsd.unprivileged_syspmcs
63is non-zero.
64.It
65Process scope.
66These PMCs only measure hardware events when the processes they are
67attached to are executing on a CPU.
68In an SMP system, process scope PMCs migrate between CPUs along with
69their target processes.
70.El
71.Pp
72Orthogonal to PMC scope, PMCs may be allocated in one of two
73operational modes:
74.Bl -bullet
75.It
76Counting PMCs measure events according to their scope
77(system or process).
78The application needs to explicitly read these counters
79to retrieve their value.
80.It
81Sampling PMCs cause the CPU to be periodically interrupted
82and information about its state of execution to be collected.
83Sampling PMCs are used to profile specific processes and kernel
84threads or to profile the system as a whole.
85.El
86.Pp
87The scope and operational mode for a software PMC are specified at
88PMC allocation time.
89An application is allowed to allocate multiple PMCs subject
90to availability of hardware resources.
91.Pp
92The library uses human-readable strings to name the event being
93measured by hardware.
94The syntax used for specifying a hardware event along with additional
95event specific qualifiers (if any) is described in detail in section
96.Sx "EVENT SPECIFIERS"
97below.
98.Pp
99PMCs are associated with the process that allocated them and
100will be automatically reclaimed by the system when the process exits.
101Additionally, process-scope PMCs have to be attached to one or more
102target processes before they can perform measurements.
103A process-scope PMC may be attached to those target processes
104that its owner process would otherwise be permitted to debug.
105An owner process may attach PMCs to itself allowing
106it to measure its own behavior.
107Additionally, on some machine architectures, such self-attached PMCs
108may be read cheaply using specialized instructions supported by the
109processor.
110.Pp
111Certain kinds of PMCs require that a log file be configured before
112they may be started.
113These include:
114.Bl -bullet
115.It
116System scope sampling PMCs.
117.It
118Process scope sampling PMCs.
119.It
120Process scope counting PMCs that have been configured to report PMC
121readings on process context switches or process exits.
122.El
123.Pp
124Up to one log file may be configured per owner process.
125Events logged to a log file may be subsequently analyzed using the
126.Xr pmclog 3
127family of functions.
128.Ss Supported CPUs
129The CPUs known to the PMC library are named by the
130.Vt "enum pmc_cputype"
131enumeration.
132Supported CPUs include:
133.Pp
134.Bl -tag -width "Li PMC_CPU_INTEL_CORE2" -compact
135.It Li PMC_CPU_AMD_K7
136.Tn "AMD Athlon"
137CPUs.
138.It Li PMC_CPU_AMD_K8
139.Tn "AMD Athlon64"
140CPUs.
141.It Li PMC_CPU_INTEL_ATOM
142.Tn Intel
143.Tn Atom
144CPUs and other CPUs conforming to version 3 of the
145.Tn Intel
146performance measurement architecture.
147.It Li PMC_CPU_INTEL_CORE
148.Tn Intel
149.Tn Core Solo
150and
151.Tn Core Duo
152CPUs, and other CPUs conforming to version 1 of the
153.Tn Intel
154performance measurement architecture.
155.It Li PMC_CPU_INTEL_CORE2
156.Tn Intel
157.Tn "Core2 Solo" ,
158.Tn "Core2 Duo"
159and
160.Tn "Core2 Extreme"
161CPUs, and other CPUs conforming to version 2 of the
162.Tn Intel
163performance measurement architecture.
164.It Li PMC_CPU_INTEL_P5
165.Tn Intel
166.Tn "Pentium"
167CPUs.
168.It Li PMC_CPU_INTEL_P6
169.Tn Intel
170.Tn "Pentium Pro"
171CPUs.
172.It Li PMC_CPU_INTEL_PII
173.Tn "Intel Pentium II"
174CPUs.
175.It Li PMC_CPU_INTEL_PIII
176.Tn "Intel Pentium III"
177CPUs.
178.It Li PMC_CPU_INTEL_PIV
179.Tn "Intel Pentium 4"
180CPUs.
181.It Li PMC_CPU_INTEL_PM
182.Tn "Intel Pentium M"
183CPUs.
184.El
185.Ss Supported PMCs
186PMC supported by this library are named by the
187.Vt enum pmc_class
188enumeration.
189Supported PMC kinds include:
190.Pp
191.Bl -tag -width "Li PMC_CLASS_IAF" -compact
192.It Li PMC_CLASS_IAF
193Fixed function hardware counters presents in CPUs conforming to the
194.Tn Intel
195performance measurement architecture version 2 and later.
196.It Li PMC_CLASS_IAP
197Programmable hardware counters present in CPUs conforming to the
198.Tn Intel
199performance measurement architecture version 1 and later.
200.It Li PMC_CLASS_K7
201Programmable hardware counters present in
202.Tn "AMD Athlon"
203CPUs.
204.It Li PMC_CLASS_K8
205Programmable hardware counters present in
206.Tn "AMD Athlon64"
207CPUs.
208.It Li PMC_CLASS_P4
209Programmable hardware counters present in
210.Tn "Intel Pentium 4"
211CPUs.
212.It Li PMC_CLASS_P5
213Programmable hardware counters present in
214.Tn Intel
215.Tn Pentium
216CPUs.
217.It Li PMC_CLASS_P6
218Programmable hardware counters present in
219.Tn Intel
220.Tn "Pentium Pro" ,
221.Tn "Pentium II" ,
222.Tn "Pentium III" ,
223.Tn "Celeron" ,
224and
225.Tn "Pentium M"
226CPUs.
227.It Li PMC_CLASS_TSC
228The timestamp counter on i386 and amd64 architecture CPUs.
229.It Li PMC_CLASS_SOFT
230Software events.
231.El
232.Ss PMC Capabilities
233Capabilities of performance monitoring hardware are denoted using
234the
235.Vt "enum pmc_caps"
236enumeration.
237Supported capabilities include:
238.Pp
239.Bl -tag -width "Li PMC_CAP_INTERRUPT" -compact
240.It Li PMC_CAP_CASCADE
241The ability to cascade counters.
242.It Li PMC_CAP_EDGE
243The ability to count negated to asserted transitions of the hardware
244conditions being probed for.
245.It Li PMC_CAP_INTERRUPT
246The ability to interrupt the CPU.
247.It Li PMC_CAP_INVERT
248The ability to invert the sense of the hardware conditions being
249measured.
250.It Li PMC_CAP_PRECISE
251The ability to perform precise sampling.
252.It Li PMC_CAP_QUALIFIER
253The hardware allows monitored to be further qualified in some
254system dependent way.
255.It Li PMC_CAP_READ
256The ability to read from performance counters.
257.It Li PMC_CAP_SYSTEM
258The ability to restrict counting of hardware events to when the CPU is
259running privileged code.
260.It Li PMC_CAP_THRESHOLD
261The ability to ignore simultaneous hardware events below a
262programmable threshold.
263.It Li PMC_CAP_USER
264The ability to restrict counting of hardware events to those when the
265CPU is running unprivileged code.
266.It Li PMC_CAP_WRITE
267The ability to write to performance counters.
268.El
269.Ss CPU Naming Conventions
270CPUs are named using small integers from zero up to, but
271excluding, the value returned by function
272.Fn pmc_ncpu .
273On platforms supporting sparsely numbered CPUs not all the numbers in
274this range will denote valid CPUs.
275Operations on non-existent CPUs will return an error.
276.Ss Functional Grouping of the API
277This section contains a brief overview of the available functionality
278in the PMC library.
279Each function listed here is described further in its own manual page.
280.Bl -tag -width 2n
281.It Administration
282.Bl -tag -width 6n -compact
283.It Fn pmc_disable , Fn pmc_enable
284Administratively disable (enable) specific performance monitoring
285counter hardware.
286Counters that are disabled will not be available to applications to
287use.
288.El
289.It "Convenience Functions"
290.Bl -tag -width 6n -compact
291.It Fn pmc_event_names_of_class
292Returns a list of event names supported by a given PMC type.
293.It Fn pmc_name_of_capability
294Convert a
295.Dv PMC_CAP_*
296flag to a human-readable string.
297.It Fn pmc_name_of_class
298Convert a
299.Dv PMC_CLASS_*
300constant to a human-readable string.
301.It Fn pmc_name_of_cputype
302Return a human-readable name for a CPU type.
303.It Fn pmc_name_of_disposition
304Return a human-readable string describing a PMC's disposition.
305.It Fn pmc_name_of_event
306Convert a numeric event code to a human-readable string.
307.It Fn pmc_name_of_mode
308Convert a
309.Dv PMC_MODE_*
310constant to a human-readable name.
311.It Fn pmc_name_of_state
312Return a human-readable string describing a PMC's current state.
313.El
314.It "Library Initialization"
315.Bl -tag -width 6n -compact
316.It Fn pmc_init
317Initialize the library.
318This function must be called before any other library function.
319.El
320.It "Log File Handling"
321.Bl -tag -width 6n -compact
322.It Fn pmc_configure_logfile
323Configure a log file for
324.Xr hwpmc 4
325to write logged events to.
326.It Fn pmc_flush_logfile
327Flush all pending log data in
328.Xr hwpmc 4 Ns Ap s
329buffers.
330.It Fn pmc_close_logfile
331Flush all pending log data and close
332.Xr hwpmc 4 Ns Ap s
333side of the stream.
334.It Fn pmc_writelog
335Append arbitrary user data to the current log file.
336.El
337.It "PMC Management"
338.Bl -tag -width 6n -compact
339.It Fn pmc_allocate , Fn pmc_release
340Allocate (free) a PMC.
341.It Fn pmc_attach , Fn pmc_detach
342Attach (detach) a process scope PMC to a target.
343.It Fn pmc_read , Fn pmc_write , Fn pmc_rw
344Read (write) a value from (to) a PMC.
345.It Fn pmc_start , Fn pmc_stop
346Start (stop) a software PMC.
347.It Fn pmc_set
348Set the reload value for a sampling PMC.
349.El
350.It "Queries"
351.Bl -tag -width 6n -compact
352.It Fn pmc_capabilities
353Retrieve the capabilities for a given PMC.
354.It Fn pmc_cpuinfo
355Retrieve information about the CPUs and PMC hardware present in the
356system.
357.It Fn pmc_get_driver_stats
358Retrieve statistics maintained by
359.Xr hwpmc 4 .
360.It Fn pmc_ncpu
361Determine the greatest possible CPU number on the system.
362.It Fn pmc_npmc
363Return the number of hardware PMCs present in a given CPU.
364.It Fn pmc_pmcinfo
365Return information about the state of a given CPU's PMCs.
366.It Fn pmc_width
367Determine the width of a hardware counter in bits.
368.El
369.It "x86 Architecture Specific API"
370.Bl -tag -width 6n -compact
371.It Fn pmc_get_msr
372Returns the processor model specific register number
373associated with
374.Fa pmc .
375Applications may then use the x86
376.Ic RDPMC
377instruction to directly read the contents of the PMC.
378.El
379.El
380.Ss Signal Handling Requirements
381Applications using PMCs are required to handle the following signals:
382.Bl -tag -width ".Dv SIGBUS"
383.It Dv SIGBUS
384When the
385.Xr hwpmc 4
386module is unloaded using
387.Xr kldunload 8 ,
388processes that have PMCs allocated to them will be sent a
389.Dv SIGBUS
390signal.
391.It Dv SIGIO
392The
393.Xr hwpmc 4
394driver will send a PMC owning process a
395.Dv SIGIO
396signal if:
397.Bl -bullet
398.It
399If any process-mode PMC allocated by it loses all its
400target processes.
401.It
402If the driver encounters an error when writing log data to a
403configured log file.
404This error may be retrieved by a subsequent call to
405.Fn pmc_flush_logfile .
406.El
407.El
408.Ss Typical Program Flow
409.Bl -enum
410.It
411An application would first invoke function
412.Fn pmc_init
413to allow the library to initialize itself.
414.It
415Signal handling would then be set up.
416.It
417Next the application would allocate the PMCs it desires using function
418.Fn pmc_allocate .
419.It
420Initial values for PMCs may be set using function
421.Fn pmc_set .
422.It
423If a log file is necessary for the PMCs to work, it would
424be configured using function
425.Fn pmc_configure_logfile .
426.It
427Process scope PMCs would then be attached to their target processes
428using function
429.Fn pmc_attach .
430.It
431The PMCs would then be started using function
432.Fn pmc_start .
433.It
434Once started, the values of counting PMCs may be read using function
435.Fn pmc_read .
436For PMCs that write events to the log file, this logged data would be
437read and parsed using the
438.Xr pmclog 3
439family of functions.
440.It
441PMCs are stopped using function
442.Fn pmc_stop ,
443and process scope PMCs are detached from their targets using
444function
445.Fn pmc_detach .
446.It
447Before the process exits, its may release its PMCs using function
448.Fn pmc_release .
449Any configured log file may be closed using function
450.Fn pmc_configure_logfile .
451.El
452.Sh EVENT SPECIFIERS
453Event specifiers are strings comprising of an event name, followed by
454optional parameters modifying the semantics of the hardware event
455being probed.
456Event names are PMC architecture dependent, but the PMC library defines
457machine independent aliases for commonly used events.
458.Pp
459Event specifiers spellings are case-insensitive and space characters,
460periods, underscores and hyphens are considered equivalent to each other.
461Thus the event specifiers
462.Qq "Example Event" ,
463.Qq "example-event" ,
464and
465.Qq "EXAMPLE_EVENT"
466are equivalent.
467.Ss PMC Architecture Dependent Events
468PMC architecture dependent event specifiers are described in the
469following manual pages:
470.Bl -column " PMC_CLASS_TSC " "MANUAL PAGE "
471.It Em "PMC Class"      Ta Em "Manual Page"
472.It Li PMC_CLASS_IAF    Ta Xr pmc.iaf 3
473.It Li PMC_CLASS_IAP    Ta Xr pmc.atom 3 , Xr pmc.core 3 , Xr pmc.core2 3
474.It Li PMC_CLASS_K7     Ta Xr pmc.k7 3
475.It Li PMC_CLASS_K8     Ta Xr pmc.k8 3
476.It Li PMC_CLASS_P4     Ta Xr pmc.p4 3
477.It Li PMC_CLASS_P5     Ta Xr pmc.p5 3
478.It Li PMC_CLASS_P6     Ta Xr pmc.p6 3
479.It Li PMC_CLASS_TSC    Ta Xr pmc.tsc 3
480.El
481.Ss Event Name Aliases
482Event name aliases are PMC-independent names for commonly used events.
483The following aliases are known to this version of the
484.Nm pmc
485library:
486.Bl -tag -width indent
487.It Li branches
488Measure the number of branches retired.
489.It Li branch-mispredicts
490Measure the number of retired branches that were mispredicted.
491.It Li cycles
492Measure processor cycles.
493This event is implemented using the processor's Time Stamp Counter
494register.
495.It Li dc-misses
496Measure the number of data cache misses.
497.It Li ic-misses
498Measure the number of instruction cache misses.
499.It Li instructions
500Measure the number of instructions retired.
501.It Li interrupts
502Measure the number of interrupts seen.
503.It Li unhalted-cycles
504Measure the number of cycles the processor is not in a halted
505or sleep state.
506.El
507.Sh COMPATIBILITY
508The interface between the
509.Nm pmc
510library and the
511.Xr hwpmc 4
512driver is intended to be private to the implementation and may
513change.
514In order to ease forward compatibility with future versions of the
515.Xr hwpmc 4
516driver, applications are urged to dynamically link with the
517.Nm pmc
518library.
519.Pp
520The
521.Nm pmc
522API is
523.Ud
524.Sh SEE ALSO
525.Xr pmc.atom 3 ,
526.Xr pmc.core 3 ,
527.Xr pmc.core2 3 ,
528.Xr pmc.iaf 3 ,
529.Xr pmc.k7 3 ,
530.Xr pmc.k8 3 ,
531.Xr pmc.p4 3 ,
532.Xr pmc.p5 3 ,
533.Xr pmc.p6 3 ,
534.Xr pmc.soft 3 ,
535.Xr pmc.tsc 3 ,
536.Xr pmclog 3 ,
537.Xr hwpmc 4 ,
538.Xr pmccontrol 8 ,
539.Xr pmcstat 8
540.Sh HISTORY
541The
542.Nm pmc
543library first appeared in
544.Fx 6.0 .
545.Sh AUTHORS
546The
547.Lb libpmc
548library was written by
549.An "Joseph Koshy"
550.Aq jkoshy@FreeBSD.org .
551