Thread control algroithm

Split the process into 2 parts, slow start & max thread control

Slow start

Start with minimum thread 1, then for each time period, split each thread into half. Stop the process when more thread can't get us significant boost. The $THREASHOLD_1$ should be large, since this process is just rough estimate. $$ thread_t = 2\times thread_{t-1} \ |total_speed_t - 2\times total_speed_{t-1}| < THREASHOLD_1 $$

Max thread control

When we reached $THREASHOLD_1$, instead of spliting every thread, choose one task that has the longest unloaded range, then split the remaining chunk into to tasks. $$ thread_t = thread_{t-1} \ |total_speed_t - (total_speed_{t-1} + average_speed)| > THREASHOLD_2 \ thread_t < MAX_THREADS $$