pytorch

71704349 - [DDP] Allow await of custom buffer reduction in backward (#64515)

[DDP] Allow await of custom buffer reduction in backward (#64515) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/64515 For performance reasons, we would like to ensure that we can await user collectives as part of custom buffer reduction in parallel to other work. As a result, add support to return futures from custom buffer hooks and await those futures at end of backwards pass. Also added some docs to clarify how to use these APIs. ghstack-source-id: 138793803 Test Plan: I Reviewed By: zhaojuanmao Differential Revision: D30757761 fbshipit-source-id: e1a2ead9ca850cb345fbee079cf0614e91bece44