[RFC 0/2] Increase accuracy and precision of sampled io_ticks

[Josh Snyder]

Commit 5b18b5a73760 ("block: delete part_round_stats and switch to less
precise counting") introduces a sampling technique for calculating
io_ticks. The sampling algorithm introduces bias in the calculation of
I/O utilization. In my production system, this bias means that a
workload which previously reported 10% I/O utilization now reports 80%.
Patch 1 of this series eliminates the bias.

The sampling technique is also subject to statistical noise. Because it
infers io_ticks based on only 100 samples per second, io_ticks becomes
imprecise, and subject to swings when measuring both random and
deterministic workloads. Patch 2 of this series provides increased
precision by raising the sampling rate.