ruby-prof

Overview

ruby-prof is a fast code profiler for Ruby. Its features include:

Requirements

ruby-prof requires Ruby 1.8.7 or 1.9.2 and higher.

If you are running Linux or Unix you’ll need a C compiler so the extension can be compiled when it is installed.

If you are running Windows, then you may need to install the Windows specific RubyGem which includes an already built extension (see Install section).

Install

The easiest way to install ruby-prof is by using Ruby Gems. To install:

gem install ruby-prof

If you’re on windows then a prebuilt binary gem is available. You may of course compile it yourself via use of devkit on MinGW.

Usage

There are two ways of running ruby-prof, via the command line or via its API.

ruby-prof executable

The first is to use ruby-prof to run the Ruby program you want to profile. For more information refer to the documentation of the ruby-prof command.

ruby-prof API

The second way is to use the ruby-prof API to profile particular segments of code.

require 'ruby-prof'

# Profile the code
RubyProf.start
...
[code to profile]
...
result = RubyProf.stop

# Print a flat profile to text
printer = RubyProf::FlatPrinter.new(result)
printer.print(STDOUT)

Alternatively, you can use a block to tell ruby-prof what to profile:

require 'ruby-prof'

# Profile the code
result = RubyProf.profile do
  ...
  [code to profile]
  ...
end

# Print a graph profile to text
printer = RubyProf::GraphPrinter.new(result)
printer.print(STDOUT, {})

ruby-prof also supports pausing and resuming profiling runs.

require 'ruby-prof'

# Profile the code
RubyProf.start
[code to profile]
RubyProf.pause
[other code]
RubyProf.resume
[code to profile]
result = RubyProf.stop

Note that resume will automatically call start if a profiling run has not yet started. In addition, resume can also take a block:

require 'ruby-prof'

# Profile the code
RubyProf.resume do
  [code to profile]
end

data = RubyProf.stop

With this usage, resume will automatically call pause at the end of the block.

Method and Thread Elimination

ruby-prof supports eliminating specific methods and threads from profiling results. This is useful for reducing connectivity in the call graph, making it easier to identify the source of performance problems when using a graph printer.

For example, consider Integer#times: it’s hardly ever useful to know how much time is spent in the method itself. We’re much more interested in how much the passed in block contributes to the time spent in the method which contains the Integer#times call.

Methods are eliminated from the collected data by calling `eliminate_methods!` on the profiling result, before submitting it to a printer.

result = RubyProf.stop
result.eliminate_methods!([/Integer#times/])

The argument given to `eliminate_methods!` is either an array of regular expressions, or the name of a file containing a list of regular expressions (line separated text).

After eliminating methods the resulting profile will appear exactly as if those methods had been inlined at their call sites.

In a similar manner, threads can be excluded so they are not profiled at all. To do this, pass an array of threads to exclude to ruby-prof:

RubyProf::exclude_threads = [ thread2 ]
RubyProf.start

Note that the excluded threads must be specified before profiling.

Benchmarking full load time including rubygems startup cost ==

If you want to get a more accurate measurement of what takes all of a gem’s bin/xxx command to load, you may want to also measure rubygems’ startup penalty. You can do this by calling into bin/ruby-prof directly, ex:

$ gem which ruby-prof

g:/192/lib/ruby/gems/1.9.1/gems/ruby-prof-0.10.2/lib/ruby-prof.rb

now run it thus (substitute lib/ruby-prof.rb with bin/ruby-prof):

$ ruby g:/192/lib/ruby/gems/1.9.1/gems/ruby-prof-0.10.2/bin/ruby-prof g:192binsome_installed_gem_command

or

$ ruby g:/192/lib/ruby/gems/1.9.1/gems/ruby-prof-0.10.2/bin/ruby-prof ./some_file_that_does_a_require_rubygems_at_the_beginning.rb

Profiling Tests

ruby-prof supports profiling tests cases written using Ruby’s built-in unit test framework (ie, test derived from Test::Unit::TestCase). To enable profiling simply add the following line of code to within your test class:

include RubyProf::Test

Each test method is profiled separately. ruby-prof will run each test method once as a warmup and then ten additional times to gather profile data. Note that the profile data will not include the class’s setup or teardown methods.

Separate reports are generated for each method and saved, by default, in the test process’s working directory. To change this, or other profiling options, modify your test class’s PROFILE_OPTIONS hash table. To globally change test profiling options, modify RubyProf::Test::PROFILE_OPTIONS.

Profiling Rails

To profile a Rails application it is vital to run it using production like settings (cache classes, cache view lookups, etc.). Otherwise, Rail’s dependency loading code will overwhelm any time spent in the application itself (our tests show that Rails dependency loading causes a roughly 6x slowdown). The best way to do this is create a new Rails environment, profile.rb.

So to profile Rails:

  1. Create a new profile.rb environment. Make sure to turn on cache_classes and cache_template_loading. Otherwise your profiling results will be overwhelemed by the time Rails spends loading required files. You should likely turn off caching.

  2. Add the ruby-prof to your gemfile:

    group :profile do
  gem 'ruby-prof'
end

  3. Add the ruby prof rack adapter to your middleware stack. One way to do this is by adding the following code to config.ru:

    if Rails.env.profile?
  use Rack::RubyProf, :path => '/temp/profile'
end

    The path is where you want profiling results to be stored. By default the rack adapter will generate a html call graph report and flat text report.

  4. Now make a request to your running server. New profiling information will be generated for each request. Note that each request will overwrite the profiling reports created by the previous request!

Reports

ruby-prof can generate a number of different reports:

Flat profiles show the overall time spent in each method. They are a good of quickly identifying which methods take the most time. An example of a flat profile and an explanation can be found in examples/flat.txt.

There are several varieties of these – run $ ruby-prof –help

Graph profiles also show the overall time spent in each method. In addition, they also show which methods call the current method and which methods its calls. Thus they are good for understanding how methods gets called and provide insight into the flow of your program. An example text graph profile is located at examples/graph.txt.

HTML Graph profiles are the same as graph profiles, except output is generated in hyper-linked HTML. Since graph profiles can be quite large, the embedded links make it much easier to navigate the results. An example html graph profile is located at examples/graph.html.

Call graphs output results in the calltree profile format which is used by KCachegrind. Call graph support was generously donated by Carl Shimer. More information about the format can be found at the KCachegrind site.

Call stack reports produce a HTML visualization of the time spent in each execution path of the profiled code. An example can be found at examples/stack.html.

Another good example: [twitpic.com/28z94a]

Finally, there’s a so called MultiPrinter which can generate several reports in one profiling run. See examples/multi.stack.html.

There is also a graphviz .dot visualiser.

Printers

Reports are created by printers. Supported printers include:

To use a printer:

...
result = RubyProf.stop
printer = RubyProf::GraphPrinter.new(result)
printer.print(STDOUT, :min_percent => 2)

The first parameter is any writable IO object such as STDOUT or a file. The second parameter, specifies the minimum percentage a method must take to be printed. Percentages should be specified as integers in the range 0 to 100. For more information please see the documentation for the different printers.

The other option is :print_file => true (default false), which adds the filename to the output (GraphPrinter only).

The MultiPrinter differs from the other printers in that it requires a directory path and a basename for the files it produces.

printer = RubyProf::MultiPrinter.new(result)
printer.print(:path => ".", :profile => "profile")

Measurements

Depending on the mode and platform, ruby-prof can measure various aspects of a Ruby program. Supported measurements include:

Process time measures the time used by a process between any two moments. It is unaffected by other processes concurrently running on the system. Note that Windows does not support measuring process times - therefore, measurements on Windows defaults to wall time.

Wall time measures the real-world time elapsed between any two moments. If there are other processes concurrently running on the system that use significant CPU or disk time during a profiling run then the reported results will be too large.

CPU time uses the CPU clock counter to measure time. The returned values are dependent on the correctly setting the CPU’s frequency. This mode is only supported on Pentium or PowerPC platforms (linux only).

Object allocation reports show how many objects each method in a program allocates. This support was added by Sylvain Joyeux and requires a patched Ruby interpreter. For more information and the patch, please see: rubyforge.org/tracker/index.php?func=detail&aid=11497&group_id=426&atid=1700

Memory usage reports show how much memory each method in a program uses. This support was added by Alexander Dymo and requires a patched Ruby interpreter. For more information, see: rubyforge.org/tracker/index.php?func=detail&aid=17676&group_id=1814&atid=7062

Garbage collection runs report how many times Ruby’s garbage collector is invoked during a profiling session. This support was added by Jeremy Kemper and requires a patched Ruby interpreter. For more information, see: rubyforge.org/tracker/index.php?func=detail&aid=17676&group_id=1814&atid=7062

Garbage collection time reports how much time is spent in Ruby’s garbage collector during a profiling session. This support was added by Jeremy Kemper and requires a patched Ruby interpreter. For more information, see: rubyforge.org/tracker/index.php?func=detail&aid=17676&group_id=1814&atid=7062

To set the measurement:

The default value is RubyProf::PROCESS_TIME.

You may also specify the measure_mode by using the RUBY_PROF_MEASURE_MODE environment variable:

On Linux, process time is measured using the clock method provided by the C runtime library. Note that the clock method does not report time spent in the kernel or child processes and therefore does not measure time spent in methods such as Kernel.sleep method. If you need to measure these values, then use wall time. Wall time is measured using the gettimeofday kernel method.

On Windows, timings default to wall times. If you set the clock mode to PROCESS_TIME, then timing are read using the clock method provided by the C runtime library. Note though, these values are wall times on Windows and not process times like on Linux. Wall time is measured using the GetLocalTime API.

If you use wall time, the results will be affected by other processes running on your computer, network delays, disk access, etc. As result, for the best results, try to make sure your computer is only performing your profiling run and is otherwise quiescent.

On both platforms, cpu time is measured using the RDTSC assembly function provided by the Pentium and PowerPC platforms. CPU time is dependent on the cpu’s frequency. On Linux, ruby-prof attempts to read this value from “/proc/cpuinfo.” On Windows, you must manually specify the clock frequency. This can be done using the RUBY_PROF_CPU_FREQUENCY environment variable:

export RUBY_PROF_CPU_FREQUENCY=<value>

You can also directly set the cpu frequency by calling:

RubyProf.cpu_frequency = <value>

Multi-threaded Applications

Unfortunately, Ruby does not provide an internal api for detecting thread context switches in 1.8. As a result, the timings ruby-prof reports for each thread may be slightly inaccurate. In particular, this will happen for newly spawned threads that go to sleep immediately (their first call). For instance, if you use Ruby’s timeout library to wait for 2 seconds, the 2 seconds will be assigned to the foreground thread and not the newly created background thread. These errors can largely be avoided if the background thread performs any operation before going to sleep.

Performance

Significant effort has been put into reducing ruby-prof’s overhead as much as possible. Our tests show that the overhead associated with profiling code varies considerably with the code being profiled. Most programs will run approximately twice as slow while highly recursive programs (like the fibonacci series test) will run three times slower.

License

See LICENSE for license information.

Development

Code is located at github.com/rdp/ruby-prof

Google group/mailing list: groups.google.com/group/ruby-optimization