GitLab

Summary:
Added `--fast-stat-sync` option.
This avoids pickle and achieves `~7%` more `wps` on 16 nodes.
It is less flexible as it just aggregates only basic stats and it ignores the aggregate function defined by criterion.

Let me know what you think myleott
Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/858

Differential Revision: D17398770

fbshipit-source-id: 36261a1d970e67deeda8211af8f009ef9b4f9c14