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pprof

pprof is a tool for visualization and analysis of profiling data.

pprof reads a collection of profiling samples in profile.proto format and generates reports to visualize and help analyze the data. It can generate both text and graphical reports (through the use of the dot visualization package).

profile.proto is a protocol buffer that describes a set of callstacks and symbolization information. A common usage is to represent a set of sampled callstacks from statistical profiling. The format is described on the proto/profile.proto file. For details on protocol buffers, see https://developers.google.com/protocol-buffers

Profiles can be read from a local file, or over http. Multiple profiles of the same type can be aggregated or compared.

If the profile samples contain machine addresses, pprof can symbolize them through the use of the native binutils tools (addr2line and nm).

pprof profiles

pprof operates on data in the profile.proto format. Each profile is a collection of samples, where each sample is associated to a point in a location hierarchy, one or more numeric values, and a set of labels. Often these profiles represents data collected through statistical sampling of a program, so each sample describes a program call stack and a number or value of samples collected at a location. pprof is agnostic to the profile semantics, so other uses are possible. The interpretation of the reports generated by pprof depends on the semantics defined by the source of the profile.

Usage modes

There are few different ways of using pprof.

Report generation

If a report format is requested on the command line:

pprof <format> [options] source

pprof will generate a report in the specified format and exit. Formats can be either text, or graphical. See below for details about supported formats, options, and sources.

Interactive terminal use

Without a format specifier:

pprof [options] source

pprof will start an interactive shell in which the user can type commands. Type help to get online help.

Web interface

If a host:port is specified on the command line:

pprof -http=[host]:[port] [options] source

pprof will start serving HTTP requests on the specified port. Visit the HTTP url corresponding to the port (typically http://<host>:<port>/) in a browser to see the interface.

Details

The objective of pprof is to generate a report for a profile. The report is generated from a location hierarchy, which is reconstructed from the profile samples. Each location contains two values:

  • flat: the value of the location itself.
  • cum: the value of the location plus all its descendants.

Samples that include a location multiple times (e.g. for recursive functions) are counted only once per location.

Options

options configure the contents of a report. Each option has a value, which can be boolean, numeric, or strings. While only one format can be specified, most options can be selected independently of each other.

Some common pprof options are:

  • -flat [default], -cum: Sort entries based on their flat or cumulative value respectively, on text reports.
  • -functions [default], -filefunctions, -files, -lines, -addresses: Generate the report using the specified granularity.
  • -noinlines: Attribute inlined functions to their first out-of-line caller. For example, a command like pprof -list foo -noinlines profile.pb.gz can be used to produce the annotated source listing attributing the metrics in the inlined functions to the out-of-line calling line.
  • -nodecount= int: Maximum number of entries in the report. pprof will only print this many entries and will use heuristics to select which entries to trim.
  • -focus= regex: Only include samples that include a report entry matching regex.
  • -ignore= regex: Do not include samples that include a report entry matching regex.
  • -show_from= regex: Do not show entries above the first one that matches regex.
  • -show= regex: Only show entries that match regex.
  • -hide= regex: Do not show entries that match regex.

Each sample in a profile may include multiple values, representing different entities associated to the sample. pprof reports include a single sample value, which by convention is the last one specified in the report. The sample_index= option selects which value to use, and can be set to a number (from 0 to the number of values - 1) or the name of the sample value.

Sample values are numeric values associated to a unit. If pprof can recognize these units, it will attempt to scale the values to a suitable unit for visualization. The unit= option will force the use of a specific unit. For example, unit=sec will force any time values to be reported in seconds. pprof recognizes most common time and memory size units.

Tags

Samples in a profile may have tags. These tags have a name and a value. The value can be either numeric or a string; the numeric values can be associated with a unit. Tags are used as additional dimensions that the sample values can be broken by. The most common use of tags is selecting samples from a profile based on the tag values. pprof also supports tags at the visualization time.

Tag filtering

The -tagfocus option is the most used option for selecting data in a profile based on tag values. It has the syntax of -tagfocus=regex or -tagfocus=range: which will restrict the data to samples with tags matched by regexp or in range. The -tagignore option has the identical syntax and can be used to filter out the samples that have matching tags. If both -tagignore and -tagfocus are specified and match a given sample, then the sample will be discarded.

When using -tagfocus=regex and -tagignore=regex, the regex will be compared to each value associated with each tag. If one specifies a value like regex1,regex2, then only samples with a tag value matching regex1 and a tag value matching regex2 will be kept.

In addition to being able to filter on tag values, one can specify the name of the tag which a certain value must be associated with using the notation -tagfocus=tagName=value. Here, the tagName must match the tag's name exactly, and the value can be either a regex or a range. If one specifies a value like regex1,regex2, then samples with a tag value (paired with the specified tag name) matching either regex1 or matching regex2 will match.

Here are examples explaining how -tagfocus can be used:

  • -tagfocus 128kb:512kb accepts a sample iff it has any numeric tag with memory value in the specified range.
  • -tagfocus mytag=128kb:512kb accepts a sample iff it has a numeric tag mytag with memory value in the specified range. There isn't a way to say -tagfocus mytag=128kb:512kb,16kb:32kb or -tagfocus mytag=128kb:512kb,mytag2=128kb:512kb. Just single value or range for numeric tags.
  • -tagfocus someregex accepts a sample iff it has any string tag with tagName:tagValue string matching specified regexp. In the future, this will change to accept sample iff it has any string tag with tagValue string matching specified regexp.
  • -tagfocus mytag=myvalue1,myvalue2 matches if either of the two tag values are present.

Tag visualization

To list the tags and their values available in a profile use -tags option. It will output the available tags and their values as well as the breakdown of the sample value by the values of each tag.

The pprof callgraph reports, such as -web or raw -dot, will automatically visualize the values for all tags as pseudo nodes in the graph. Use -tagshow and -taghide options to limit what tags are displayed. The options accept a regular expression that is matched against the tag name to show or hide it respectively.

Options -tagroot and -tagleaf can be used to create pseudo stack frames to the profile samples. For example, -tagroot=mytag will add stack frames at the root of the profile call tree with the value of the tag for the corresponding samples. Similarly, -tagleaf=mytag will add such stack frames as leaf nodes of each sample. These options are useful when visualizing a profile in tree formats such as the tree view in the -http mode web UI.

Text reports

pprof text reports show the location hierarchy in text format.

  • -text: Prints the location entries, one per line, including the flat and cum values.
  • -tree: Prints each location entry with its predecessors and successors.
  • -peek= regex: Print the location entry with all its predecessors and successors, without trimming any entries.
  • -traces: Prints each sample with a location per line.

Graphical reports

pprof can generate graphical reports on the DOT format, and convert them to multiple formats using the graphviz package.

These reports represent the location hierarchy as a graph, with a report entry represented as a node. Nodes are removed using heuristics to limit the size of the graph, controlled by the nodecount option.

  • -dot: Generates a report in .dot format. All other formats are generated from this one.
  • -svg: Generates a report in SVG format.
  • -web: Generates a report in SVG format on a temp file, and starts a web browser to view it.
  • -png, -jpg, -gif, -pdf: Generates a report in these formats.

Interpreting the Callgraph

  • Node Color:

    • large positive cum values are red.
    • large negative cum values are green; negative values are most likely to appear during profile comparison, see this section for details.
    • cum values close to zero are grey.

  • Node Font Size:

    • larger font size means larger absolute flat values.
    • smaller font size means smaller absolute flat values.

  • Edge Weight:

    • thicker edges indicate more resources were used along that path.
    • thinner edges indicate fewer resources were used along that path.

  • Edge Color:

    • large positive values are red.
    • large negative values are green.
    • values close to zero are grey.

  • Dashed Edges: some locations between the two connected locations were removed.

  • Solid Edges: one location directly calls the other.

  • "(inline)" Edge Marker: the call has been inlined into the caller.

Let's consider the following example graph:

callgraph

  • For nodes:

    • (*Rand).Read has a small flat value and a small cum value because the the font is small and the node is grey.
    • (*compressor).deflate has a large flat value and a large cum value because the font is large and the node is red.
    • (*Writer).Flush has a small flat value and a large cum value because the font is small and the node is red.

  • For edges:

    • the edge between (*Writer).Write and (*compressor).write:
      • Since it is a dashed edge, some nodes were removed between those two.
      • Since it is thick and red, more resources were used in call stacks between those two nodes.
    • the edge between (*Rand).Read and read:
      • Since it is a dashed edge, some nodes were removed between those two.
      • Since it is thin and grey, fewer resources were used in call stacks between those two nodes.
    • the edge between read and (*rngSource).Int63:
      • Since it is a solid edge, there are no nodes between those two (i.e. it was a direct call).
      • Since it is thin and grey, fewer resources were used in call stacks between those two nodes.

Annotated code

pprof can also generate reports of annotated source with samples associated to them. For these, the source or binaries must be locally available, and the profile must contain data with the appropriate level of detail.

pprof will look for source files on its current working directory and all its ancestors. pprof will look for binaries on the directories specified in the $PPROF_BINARY_PATH environment variable, by default $HOME/pprof/binaries (%USERPROFILE%\pprof\binaries on Windows). It will look binaries up by name, and if the profile includes linker build ids, it will also search for them in a directory named as the build id.

pprof uses the binutils tools to examine and disassemble the binaries. By default it will search for those tools in the current path, but it can also search for them in a directory pointed to by the environment variable $PPROF_TOOLS.

  • -list= regex: Generates an annotated source listing for functions matching regex, with flat/cum values for each source line.
  • -disasm= regex: Generates an annotated disassembly listing for functions matching regex.
  • -weblist= regex: Generates a source/assembly combined annotated listing for functions matching regex, and starts a web browser to display it.

Comparing profiles

pprof can subtract one profile from another, provided the profiles are of compatible types (i.e. two heap profiles). pprof has two options which can be used to specify the filename or URL for a profile to be subtracted from the source profile:

  • -diff_base= profile: useful for comparing two profiles. Percentages in the output are relative to the total of samples in the diff base profile.

  • -base= profile: useful for subtracting a cumulative profile, like a golang block profile, from another cumulative profile collected from the same program at a later time. When comparing cumulative profiles collected on the same program, percentages in the output are relative to the difference between the total for the source profile and the total for the base profile.

The -normalize flag can be used when a base profile is specified with either the -diff_base or the -base option. This flag scales the source profile so that the total of samples in the source profile is equal to the total of samples in the base profile prior to subtracting the base profile from the source profile. Useful for determining the relative differences between profiles, for example, which profile has a larger percentage of CPU time used in a particular function.

When using the -diff_base option, some report entries may have negative values. If the merged profile is output as a protocol buffer, all samples in the diff base profile will have a label with the key "pprof::base" and a value of "true". If pprof is then used to look at the merged profile, it will behave as if separate source and base profiles were passed in.

When using the -base option to subtract one cumulative profile from another collected on the same program at a later time, percentages will be relative to the difference between the total for the source profile and the total for the base profile, and all values will be positive. In the general case, some report entries may have negative values and percentages will be relative to the total of the absolute value of all samples when aggregated at the address level.

Fetching profiles

pprof can read profiles from a file or directly from a URL over http or https. Its native format is a gzipped profile.proto file, but it can also accept some legacy formats generated by gperftools.

When fetching from a URL handler, pprof accepts options to indicate how much to wait for the profile.

  • -seconds= int: Makes pprof request for a profile with the specified duration in seconds. Only makes sense for profiles based on elapsed time, such as CPU profiles.
  • -timeout= int: Makes pprof wait for the specified timeout when retrieving a profile over http. If not specified, pprof will use heuristics to determine a reasonable timeout.

pprof also accepts options which allow a user to specify TLS certificates to use when fetching or symbolizing a profile from a protected endpoint. For more information about generating these certificates, see https://docs.docker.com/engine/security/https/.

  • -tls_cert= /path/to/cert: File containing the TLS client certificate to be used when fetching and symbolizing profiles.
  • -tls_key= /path/to/key: File containing the TLS private key to be used when fetching and symbolizing profiles.
  • -tls_ca= /path/to/ca: File containing the certificate authority to be used when fetching and symbolizing profiles.

pprof also supports skipping verification of the server's certificate chain and host name when collecting or symbolizing a profile. To skip this verification, use "https+insecure" in place of "https" in the URL.

If multiple profiles are specified, pprof will fetch them all and merge them. This is useful to combine profiles from multiple processes of a distributed job. The profiles may be from different programs but must be compatible (for example, CPU profiles cannot be combined with heap profiles).

Symbolization

pprof can add symbol information to a profile that was collected only with address information. This is useful for profiles for compiled languages, where it may not be easy or even possible for the profile source to include function names or source coordinates.

pprof can extract the symbol information locally by examining the binaries using the binutils tools, or it can ask running jobs that provide a symbolization interface.

pprof will attempt symbolizing profiles by default, and its -symbolize option provides some control over symbolization:

  • -symbolize=none: Disables any symbolization from pprof.

  • -symbolize=local: Only attempts symbolizing the profile from local binaries using the binutils tools.

  • -symbolize=remote: Only attempts to symbolize running jobs by contacting their symbolization handler.

For local symbolization, pprof will look for the binaries on the paths specified by the profile, and then it will search for them on the path specified by the environment variable $PPROF_BINARY_PATH. Also, the name of the main binary can be passed directly to pprof as its first parameter, to override the name or location of the main binary of the profile, like this:

pprof /path/to/binary profile.pb.gz

By default pprof will attempt to demangle and simplify C++ names, to provide readable names for C++ symbols. It will aggressively discard template and function parameters. This can be controlled with the -symbolize=demangle option. Note that for remote symbolization mangled names may not be provided by the symbolization handler.

  • -symbolize=demangle=none: Do not perform any demangling. Show mangled names if available.

  • -symbolize=demangle=full: Demangle, but do not perform any simplification. Show full demangled names if available.

  • -symbolize=demangle=templates: Demangle, and trim function parameters, but not template parameters.

Web Interface

When the user requests a web interface (by supplying an -http=[host]:[port] argument on the command-line), pprof starts a web server and opens a browser window pointing at that server. The web interface provided by the server allows the user to interactively view profile data in multiple formats.

The top of the display is a header that contains some buttons and menus.

View

The View menu allows the user to switch between different visualizations of the profile.

Top : Displays a tabular view of profile entries. The table can be sorted interactively.

Graph : Displays a scrollable/zoomable graph view; each function (or profile entry) is represented by a node and edges connect callers to callees.

Flame Graph : Displays a view similar to a flame graph that can show the selected node's callers and callees simultaneously.

Peek : Shows callers / callees per function in a simple textual forma.

Source : Displays source code annotated with profile information. Clicking on a source line can show the disassembled machine instructions for that line.

Disassemble : Displays disassembled machine instructions annotated with profile information.

Config

The Config menu allows the user to save the current refinement settings (e.g., the focus and hide list) as a named configuration. A saved configuration can later be re-applied to reinstitue the saved refinements. The Config menu contains:

Save as ...: shows a dialog where the user can type in a configuration name. The current refinement settings are saved under the specified name.

Default: switches back to the default view by removing all refinements.

The Config menu also contains an entry per named configuration. Selecting such an entry applies that configuration. The currently selected entry is marked with a ✓. Clicking on the 🗙 on the right-hand side of such an entry deletes the configuration (after prompting the user to confirm).

Flame graph

The Flame graph view displays profile information as a flame graph.

Boxes on this view correspond to stack frames in the profile. Caller boxes are directly above callee boxes. The width of each box is proportional to the sum of the sample value of profile samples where that frame was present on the call stack. Children of a particular box are laid out left to right in decreasing size order.

Names displayed in different boxes may have different font sizes. These size differences are due to an attempt to fit as much of the name into the box as possible; no other interpretation should be placed on the size.

Boxes are colored according to the name of the package in which the corresponding function occurs. E.g., in C++ profiles all frames corresponding to std:: functions will be assigned the same color.

Inlining is indicated by the absence of a horizontal border between a caller and a callee. E.g., suppose X calls Y calls Z and the call from Y to Z is inlined into Y. There will be a black border between X and Y, but no border between Y and Z.

TODO: cover the following issues:

  • Overall layout
  • Menu entries
  • Explanation of all the views