nccl 2.4.7ms0+cuda10.0 with NCCL_SOCKET_NTHREADS=4 on 32Gbps GCE machine

root@managed-worker-3jq5:/# mpirun --allow-run-as-root -H 10.73.0.209:1,10.73.0.244:1 -np 2 -mca btl_tcp_if_include ens12 -x NCCL_IB_DISABLE=1 -x LD_LIBRARY_PATH -x NCCL_SOCKET_IFNAME=ens12 -x NCCL_DEBUG=VERSION -x NCCL_NSOCKS_PERTHREAD=1 -x NCCL_SOCKET_NTHREADS=4 /nccl-tests/build/all_reduce_perf -b 1M -e 1G -f 2 -g 1 -c 0
nThread 1 nGpus 1 minBytes 1048576 maxBytes 1073741824 step: 2(factor) warmup iters: 5 iters: 20 validation: 0
NCCL version 2.4.7ms0+cuda10.0
# NCCL Tests compiled with NCCL 2.4
# Using devices
#   Rank  0 on managed-worker-3jq5 device  0 [0x00] Tesla V100-SXM2-16GB

#                                                 out-of-place                    in-place
#      bytes             N    type      op     time  algbw  busbw      res     time  algbw  busbw      res
#   Rank  1 on managed-worker-0khr device  0 [0x00] Tesla V100-SXM2-16GB
     1048576        262144   float     sum    2.059   0.51   0.51  	N/A    3.314   0.32   0.32  	N/A
     2097152        524288   float     sum    3.047   0.69   0.69  	N/A    6.873   0.31   0.31  	N/A
     4194304       1048576   float     sum    5.074   0.83   0.83  	N/A    5.525   0.76   0.76  	N/A
     8388608       2097152   float     sum    7.145   1.17   1.17  	N/A    8.716   0.96   0.96  	N/A
    16777216       4194304   float     sum   17.616   0.95   0.95  	N/A   17.165   0.98   0.98  	N/A
    33554432       8388608   float     sum   37.980   0.88   0.88  	N/A   35.914   0.93   0.93  	N/A
    67108864      16777216   float     sum   68.106   0.99   0.99  	N/A   72.205   0.93   0.93  	N/A
   134217728      33554432   float     sum  169.402   0.79   0.79  	N/A  121.435   1.11   1.11  	N/A
   268435456      67108864   float     sum  243.531   1.10   1.10  	N/A  252.268   1.06   1.06  	N/A
   536870912     134217728   float     sum  497.448   1.08   1.08  	N/A  519.911   1.03   1.03  	N/A
  1073741824     268435456   float     sum  962.883   1.12   1.12  	N/A  970.829   1.11   1.11  	N/A
 Out of bounds values : 0 OK
 Avg bus bandwidth    : 0.89094