* set a minimal reducer msg size. Receive the same data size from parent each time.
* When parent read from a child, check it receive minimal reduce size.
fix bug. Rewrite the minimal reducer size check, make sure it's 1~N times of minimal reduce size
Assume the minimal reduce size is X, the logic here is
1: each child upload total_size of message
2: each parent receive X message at least, up to total_size
3: parent reduce X or NxX or total_size message
4: parent sends X or NxX or total_size message to its parent
4: parent's parent receive X message at least, up to total_size. Then reduce X or NxX or total_size message
6: parent's parent sends X or NxX or total_size message to its children
7: parent receives X or NxX or total_size message, sends to its children
8: child receive X or NxN or total_size message.
During the whole process, each transfer is (1~N)xX Byte message or up to total_size.
if X is larger than total_size, then allreduce allways reduce the whole messages and pass down.
* Follow style check rule
* fix the cpplint check
* fix allreduce_base header seq
Co-authored-by: Philip Hyunsu Cho <chohyu01@cs.washington.edu>
FelixYBW
