Enable raw stackprof collection for flamegraphs

Also add documentation on how to generate flamegraphs.

bin/rspec-stackprof

@@ -8,9 +8,10 @@ require 'spec_helper'
 filename = ARGV[0].split('/').last
 interval = ENV.fetch('INTERVAL', 1000).to_i
 limit = ENV.fetch('LIMIT', 20)
+raw = ENV.fetch('RAW', false) == 'true'
 output_file = "tmp/#{filename}.dump"
 
-StackProf.run(mode: :wall, out: output_file, interval: interval) do
+StackProf.run(mode: :wall, out: output_file, interval: interval, raw: raw) do
   RSpec::Core::Runner.run(ARGV, $stderr, $stdout)
 end
 

doc/development/performance.md

@@ -173,11 +173,30 @@ dot -Tsvg project_policy_spec.dot > project_policy_spec.svg
 To load the profile in [kcachegrind](https://kcachegrind.github.io/):
 
 ```shell
-stackprof tmp/project_policy_spec.dump --callgrind > project_policy_spec.callgrind
+stackprof tmp/project_policy_spec.rb.dump --callgrind > project_policy_spec.callgrind
 kcachegrind project_policy_spec.callgrind # Linux
 qcachegrind project_policy_spec.callgrind # Mac
 ```
 
+For flamegraphs, enable raw collection first. Note that raw
+collection can generate a very large file, so increase the `INTERVAL`, or
+run on a smaller number of specs for smaller file size:
+
+```shell
+RAW=true bin/rspec-stackprof spec/policies/group_member_policy_spec.rb
+```
+
+You can then generate, and view the resultant flamegraph. It might take a
+while to generate based on the output file size:
+
+```shell
+# Generate
+stackprof --flamegraph tmp/group_member_policy_spec.rb.dump > group_member_policy_spec.flame
+
+# View
+stackprof --flamegraph-viewer=group_member_policy_spec.flame
+```
+
 It may be useful to zoom in on a specific method, for example:
 
 ```shell