profile.rb

puts <<EOS
[    0.000000] event foo.bar START
[    0.500000] some other generic log that should be ignored
[    1.000000] event foo.bar STOP
[    2.000000] event foo.bar START
[    5.000000] event foo.bar STOP
[    6.000000] event foo.qux START
[    7.000000] event foo.qux STOP
EOS
  .split("\n")
  .lazy
  .select {|line| line =~ /\[(.*)\] event (.*) (START|STOP)/}
  .map { {:event => $2, :ts => $1.to_f, :start => $3 == "START"} }
  .chunk {|event| event[:event]}
  .map { |chunk|
    name, events = chunk
    deltas = events.lazy
      .each_slice(2)
      .map {|slice| slice.last[:ts] - slice.first[:ts]}
    "Event #{name}: max #{deltas.max}, average #{deltas.reduce(&:+) / deltas.size}"
  }
  .force