The client concurrency will affect this. Set the parameters with:

osc..max_pages_per_rpc=1048576
osc..max_rpcs_in_flight=256

The test env is : 6 clients 3 servers

In the io500.sh, we can setup some parameters for client like this:

Lustre Client Setting

$PDSH -w ${LUSTRE_CLIENT} lctl set_param
osc..max_pages_per_rpc=1048576
osc..max_rpcs_in_flight=256
osc..max_dirty_mb=2000
osc..checksums=0
osc..short_io_bytes=65536
llite..max_read_ahead_mb=2048
llite..max_read_ahead_per_file_mb=16
llite..max_cached_mb=8192
ldlm.namespaces..lru_size=0
ldlm.namespaces..lru_max_age=5000
mdc..max_rpcs_in_flight=128
mdc..max_mod_rpcs_in_flight=8

Then the software lockup will disappear.