[gemini] async grad chunk reduce (all-reduce&reduce-scatter)

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trace

previous

now

benchmark

before

colossalai run --nproc_per_node 8 --hostfile hosts.txt benchmark.py -g -x -b 4 -s 100

num_samples: 392, dp_world_size: 8, flop_megatron: 9.7808637396779e+16, flop: 86555325938794496, avg_duration: 567.2686767578125, avg_throughput: 5.528244601700203
Throughput: 5.53 samples/sec, TFLOPS per GPU by Megatron: 172.42, TFLOPS per GPU: 152.58
Max CUDA memory usage: 53503.48 MB

now

colossalai run --nproc_per_node 8 --hostfile hosts.txt benchmark.py -g -x -b 4 -s 100 --async-reduce

num_samples: 392, dp_world_size: 8, flop_megatron: 9.7808637396779e+16, flop: 86555325938794496, avg_duration: 562.5335083007812, avg_throughput: 5.574779019782774
Throughput: 5.57 samples/sec, TFLOPS per GPU by Megatron: 173.87, TFLOPS per GPU: 153.87
Max CUDA memory usage: 53504.40 MB