G1 logs summary stats such as min, max, avg, etc.. for all the parallel GC workers. I am only tracking avg and max as the others are not very useful to debug perf issues. Below is a sample extract from a g1 gc log showing the summary stats

[Parallel Time: 18.3 ms, GC Workers: 18]
      [GC Worker Start (ms): Min: 11303.7, Avg: 11304.8, Max: 11305.7, Diff: 2.0]
      [Ext Root Scanning (ms): Min: 0.6, Avg: 2.1, Max: 9.8, Diff: 9.1, Sum: 37.4]
      [Update RS (ms): Min: 0.0, Avg: 0.0, Max: 0.2, Diff: 0.2, Sum: 0.2]
         [Processed Buffers: Min: 0, Avg: 2.4, Max: 34, Diff: 34, Sum: 44]
      [Scan RS (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 1.1]
      [Object Copy (ms): Min: 6.6, Avg: 13.2, Max: 14.3, Diff: 7.7, Sum: 236.8]
      [Termination (ms): Min: 0.0, Avg: 0.8, Max: 1.0, Diff: 1.0, Sum: 15.2]
      [GC Worker Other (ms): Min: 0.0, Avg: 0.1, Max: 0.2, Diff: 0.2, Sum: 0.9]
      [GC Worker Total (ms): Min: 15.2, Avg: 16.2, Max: 17.2, Diff: 2.0, Sum: 291.6]
      [GC Worker End (ms): Min: 11320.9, Avg: 11321.0, Max: 11321.1, Diff: 0.2]