Wrong CPU Time shown in Instruments

I have 2 questions with Xcode's Instruments.
  1. I have filtered 30s in track, but the CPU Time shown below is much more than 30s. It is not standed for the whole track either because it will change when I change the filter above.

  2. machkernel uses 57.1% CPU and mediaserverd uses 24.9%, but machkernel's CPU time is thrible more of mediaserverd. Why the proportion of %CPU is not equal to CPU time?

!Here is the image