Make pp_stream wait on attn_backward_dx #10984
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lshpku force-pushed the fix-pp-event-wait branch from b78af3d to b6e9841 Compare lshpku force-pushed the fix-pp-event-wait branch from b6e9841 to 1b1e63a Compare 
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PR types
Bug fixes
PR changes
Models
Description
让 pp_stream 等待 attn_backward_dx，解决开启 overlap_p2p_comm 时遇到的 loss 下降速度慢的问题
下图显示了修复前和修复后的等待关系
其实我也不知道为什么加这条等待就行，我只是通过二分法定位到是 PP(F) 的问题，然后试着加了等待，然后 loss 就正常了，估计跟跨 stream 分配显存有关，我通过单测发现 Paddle 的跨 stream 分配显存有一些不安全的情况，虽然模型里看起来没有不安全的用法，但也不好说，所以还是保守一点
对性能有一定影响，因为把 PP(F) 推后了，该 PR 还需要改进
正常情况下，单机配置（29 Decoder + 1 MTP），跑200个step，loss应该下降到7.3；在本PR之前开启 overlap_p2p_comm，loss 只能降到8.7；现在开不开都能降到7.3