Add piece per chunk multiplier to chunk download.
Created by: RNabel
- Adds a multiplier determining the maximum number of pieces per chunk to be downloaded concurrently relative to the minimum required,
- Adds a limiter to the number of chunks to which this new maximum is applied. The limiter controls that the speed up is only applied to the last N chunks.
This PR has resulted in single-chunk download times to go from ~19s to as low as 2.2s (multiplier val: 2.5). The current multiplier results in speedups of about 3-4x to <5s.
Disclaimer: these measurements were made on a Gbit network with direct connection to the internet backbone.