Adding SHOW_PERCENTILES to show extra per-iteration statistics

[gilbertlee-amd]

Motivation

Add ability to get additional statistics about per-iteration duration through the new env var SHOW_PERCENTILES which takes in comma-separated percentages. For example SHOW_PERCENTILES=50,90,99 reports the duration 50%/90%/99% of Transfers are faster than.

Technical Details

This is purely a client-side change. When SHOW_PERCENTILES is enabled, per-iteration timing is recorded, and then the results are sorted to compute the statistics:

Example output

Test 1:

-------------------┬--------------┬------------┬-------------------┬--------------------
  Executor: CPU 00 │  12.058 GB/s │  89.050 ms │  1073741824 bytes │  12.091 GB/s (sum)
-------------------┼--------------┼------------┼-------------------┼--------------------
     Transfer 0    │  12.091 GB/s │  88.802 ms │  1073741824 bytes │ C0 -> C0:1 -> C1
               p50 │  12.090 GB/s │  88.814 ms │                   │
               p90 │  11.720 GB/s │  91.617 ms │                   │
               p99 │  11.702 GB/s │  91.757 ms │                   │
-------------------┼--------------┼------------┼-------------------┼--------------------
   Aggregate (CPU) │  12.014 GB/s │  89.374 ms │  1073741824 bytes │ Overhead 0.325 ms
-------------------┴--------------┴------------┴-------------------┴--------------------