Two A100 nodes cannot reach ideal all-reduce performance
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Description
Hello,
We ary trying to test all-reduce performance for A100 of two nodes, eyery node the configuration is as follows:
A100 * 8, IB 200Gb * 4 (dual port),
We tested three scenarios:
- ib_bw_write of NIC within two nodes
- singleNode, ./build/all_reduce_perf -b 8 -e 4G -f 2 -g 8, result: 232.54GB/s
- nccl all-reduce between two nodes only 86GB/s。There is a big gap compared to the theoretical value(100 GB/s), why is this?
log:
test.log
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Research direction
Start with the attached test.log and the reported all_reduce_perf command; compare the single-node and two-node measurements with the A100 and InfiniBand topology described. Use the all_reduce_perf entry point to investigate the reported gap. Done means a reproducible diagnosis and a validated two-node performance result.
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Assessment
- Domain
- distributed-systems, networking, performance
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100