Implement xm.rendezvous with XLA collective communication - #4181
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I tested this on v4-8 and v4-4096 and it seems to work successfully on both accelerator types. Using |
JackCaoG
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Anything in the PJRT README we should update?
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I'll update the readme after #4193 |
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We have found that
gloodoesn't scale effectively to large pod sizes, and it's not easily possible to usetorch.distributedin a multithreaded context such as TPU v3.xm.rendezvouswill now callxm.mark_stepto sync results from XLA.xm.rendezvous. Also remove initialization based onXRT_MESH_SERVICE_ADDRESSsince host 0 is not predictable anyway.xm.rendezvousfrom all replicas per XLA requirements:Computing the result of AllReduce requires having one input from each replica, so if one replica executes a AllReduce node more times than another, then the former replica will wait forever.This covers the vast majority of the usage ofrendezvousin our experience.Tested manually on a TPU v4-8 with 1 process and 4 threads to simulate a v3.