NAME

pmcstat — performance measurement with performance monitoring hardware

SYNOPSIS

DESCRIPTION

The pmcstat utility measures system performance using the facilities provided by hwpmc(4).

The pmcstat utility can measure both hardware events seen by the system as a whole, and those seen when a specified set of processes are executing on the system's CPUs. If a specific set of processes is being targeted (for example, if the -t process-spec option is specified, or if a command line is specified using command), then measurement occurs till command exits, or till all target processes specified by the -t process-spec options exit, or till the pmcstat utility is interrupted by the user. If a specific set of processes is not targeted for measurement, then pmcstat will perform system-wide measurements till interrupted by the user.

A given invocation of pmcstat can mix allocations of system-mode and process-mode PMCs, of both counting and sampling flavors. The values of all counting PMCs are printed in human readable form at regular intervals by pmcstat. The output of sampling PMCs may be configured to go to a log file for subsequent offline analysis, or, at the expense of greater overhead, may be configured to be printed in text form on the fly.

Hardware events to measure are specified to pmcstat using event specifier strings event-spec. The syntax of these event specifiers is machine dependent and is documented in pmc(3).

A process-mode PMC may be configured to be inheritable by the target process' current and future children.

OPTIONS

The following options are available:

-C

Toggle between showing cumulative or incremental counts for subsequent counting mode PMCs specified on the command line. The default is to show incremental counts.

-D pathname

Create files with per-program samples in the directory named by pathname. The default is to create these files in the current directory.

-E

Toggle showing per-process counts at the time a tracked process exits for subsequent process-mode PMCs specified on the command line. This option is useful for mapping the performance characteristics of a complex pipeline of processes when used in conjunction with the -d option. The default is to not to enable per-process tracking.

-F pathname

Print calltree (Kcachegrind) information to file pathname. If argument pathname is a “-” this information is sent to the output file specified by the -o option.

-G pathname

Print callchain information to file pathname. If argument pathname is a “-” this information is sent to the output file specified by the -o option.

-I

Skip symbol lookup and display address instead.

-L

List all event names.

-M mapfilename

Write the mapping between executable objects encountered in the event log and the abbreviated pathnames used for gprof(1) profiles to file mapfilename. If this option is not specified, mapping information is not written. Argument mapfilename may be a “-” in which case this mapping information is sent to the output file configured by the -o option.

-N

Toggle capturing callchain information for subsequent sampling PMCs. The default is for sampling PMCs to capture callchain information.

-O logfilename

Send logging output to file logfilename. If logfilename is of the form hostname:port, where hostname does not start with a ‘.’ or a ‘/’, then pmcstat will open a network socket to host hostname on port port.

If the -O option is not specified and one of the logging options is requested, then pmcstat will print a textual form of the logged events to the configured output file.

-P event-spec

Allocate a process mode sampling PMC measuring hardware events specified in event-spec.

-R logfilename

Perform offline analysis using sampling data in file logfilename.

-S event-spec

Allocate a system mode sampling PMC measuring hardware events specified in event-spec.

-T

Use a top like mode for sampling PMCs. The following hotkeys can be used: 'c+a' switch to accumulative mode, 'c+d' switch to delta mode, 'm' merge PMCs, 'n' change view, 'p' show next PMC, ' ' pause, 'q' quit. calltree only: 'f' cost under threshold is seen as a dot.

-U

Toggle capturing user-space call traces while in kernel mode. The default is for sampling PMCs to capture user-space callchain information while in user-space mode, and kernel callchain information while in kernel mode.

-W

Toggle logging the incremental counts seen by the threads of a tracked process each time they are scheduled on a CPU. This is an experimental feature intended to help analyse the dynamic behaviour of processes in the system. It may incur substantial overhead if enabled. The default is for this feature to be disabled.

-a pathname

Perform a symbol and file:line lookup for each address in each callgraph and save the output to pathname. Unlike -m that only resolves the first symbol in the graph, this resolves every node in the callgraph, or prints out addresses if no lookup information is available. This option requires the -R option to read in samples that were previously collected and saved with the -O option.

-c cpu-spec

Set the cpus for subsequent system mode PMCs specified on the command line to cpu-spec. Argument cpu-spec is a comma separated list of CPU numbers, or the literal ‘*’ denoting all available CPUs. The default is to allocate system mode PMCs on all available CPUs.

-d

Toggle between process mode PMCs measuring events for the target process' current and future children or only measuring events for the target process. The default is to measure events for the target process alone. (it has to be passed in the command line prior to -p, -s, -P, or -S).

-e

Specify that the gprof profile files will use a wide history counter. These files are produced in a format compatible with gprof(1). However, other tools that cannot fully parse a BSD-style gmon header might be unable to correctly parse these files.

-f pluginopt

Pass option string to the active plugin.
threshold=<float> do not display cost under specified value (Top).
skiplink=0|1 replace node with cost under threshold by a dot (Top).

-g

Produce profiles in a format compatible with gprof(1). A separate profile file is generated for each executable object encountered. Profile files are placed in sub-directories named by their PMC event name.

-i lwp

Filter on thread ID lwp, which you can get from ps(1) -o lwp.

-k kerneldir

Set the pathname of the kernel directory to argument kerneldir. This directory specifies where pmcstat should look for the kernel and its modules. The default is to use the path of the running kernel obtained from the kern.bootfile sysctl.

-l secs

Set system-wide performance measurement duration for secs seconds. The argument secs may be a fractional value.

-m pathname

Print the sampled PCs with the name, the start and ending addresses of the function within they live. The pathname argument is mandatory and indicates where the information will be stored. If argument pathname is a “-” this information is sent to the output file specified by the -o option. This option requires the -R option to read in samples that were previously collected and saved with the -O option.

-n rate

Set the default sampling rate for subsequent sampling mode PMCs specified on the command line. The default is to configure PMCs to sample the CPU's instruction pointer every 65536 events.

-o outputfile

Send counter readings and textual representations of logged data to file outputfile. The default is to send output to stderr when collecting live data and to stdout when processing a pre-existing logfile.

-p event-spec

Allocate a process mode counting PMC measuring hardware events specified in event-spec.

-q

Decrease verbosity.

-r fsroot

Set the top of the filesystem hierarchy under which executables are located to argument fsroot. The default is /.

-s event-spec

Allocate a system mode counting PMC measuring hardware events specified in event-spec.

-t process-spec

Attach process mode PMCs to the processes named by argument process-spec. Argument process-spec may be a non-negative integer denoting a specific process id, or a regular expression for selecting processes based on their command names.

-u event-spec

Provide short description of event.

-v

Increase verbosity.

-w secs

Print the values of all counting mode PMCs or sampling mode PMCs for top mode every secs seconds. The argument secs may be a fractional value. The default interval is 5 seconds.

-z graphdepth

When printing system-wide callgraphs, limit callgraphs to the depth specified by argument graphdepth.

If command is specified, it is executed using execvp(3).

EXAMPLES

To perform system-wide statistical sampling on an AMD Athlon CPU with samples taken every 32768 instruction retirals and data being sampled to file sample.stat, use:

To execute firefox and measure the number of data cache misses suffered by it and its children every 12 seconds on an AMD Athlon, use:

To measure instructions retired for all processes named “emacs” use:

To measure instructions retired for processes named “emacs” for a period of 10 seconds use:

To count instruction tlb-misses on CPUs 0 and 2 on a Intel Pentium Pro/Pentium III SMP system use:

To collect profiling information for a specific process with pid 1234 based on instruction cache misses seen by it use:

To perform system-wide sampling on all configured processors based on processor instructions retired use:

To send the generated event log to a remote machine use:

To generate gprof(1) compatible profiles from a sample file use:

To print a system-wide profile with callgraphs to file foo.graph use:

DIAGNOSTICS

If option -v is specified, pmcstat may issue the following diagnostic messages:

#callchain/dubious-frames

The number of callchain records that had an “impossible” value for a return address.

#exec handling errors

The number of exec(2) events in the log file that named executables that could not be analyzed.

#exec/elf

The number of exec(2) events that named ELF executables.

#exec/unknown

The number of exec(2) events that named executables with unrecognized formats.

#samples/total

The total number of samples in the log file.

#samples/unclaimed

The number of samples that could not be correlated to a known executable object (i.e., to an executable, shared library, the kernel or the runtime loader).

#samples/unknown-object

The number of samples that were associated with an executable with an unrecognized object format.

The pmcstat utility exits 0 on success, and >0 if an error occurs.

COMPATIBILITY

Due to the limitations of the gmon.out file format, gprof(1) compatible profiles generated by the -g option do not contain information about calls that cross executable boundaries. The generated gmon.out files are also only meaningful for native executables.

SEE ALSO

gprof(1), nc(1), execvp(3), pmc(3), pmclog(3), hwpmc(4), pmccontrol(8), sysctl(8)

HISTORY

The pmcstat utility first appeared in FreeBSD 6.0. It is currently under development.

AUTHORS

Joseph Koshy <jkoshy@FreeBSD.org>

BUGS

The pmcstat utility cannot yet analyse hwpmc(4) logs generated by non-native architectures.