`hdr_value_at_percentile()` is part of the Hdr_Histogram library
used when generating `latencystats` report.
There's a pending optimization for this function which greatly
affects the performance of `info latencystats`.
https://github.com/HdrHistogram/HdrHistogram_c/pull/107
This PR:
1. Upgrades the sources in _deps/hdr_histogram_ to the latest Hdr_Histogram
version 0.11.5
2. Applies the referenced optimization.
3. Adds minor documentation about the hdr_histogram dependency which was
missing under _deps/README.md_.
benchmark on my machine:
running: `redis-benchmark -n 100000 info latencystats` on a clean build with no data.
| benchmark | RPS |
| ---- | ---- |
| before upgrade to v0.11.05 | 7,681 |
| before optimization | 12,474 |
| after optimization | 52,606 |
Co-authored-by: filipe oliveira <filipecosta.90@gmail.com>
