Description of problem:
Having the infiniband stack and perhaps more especificly mlx5_ib driver loaded causes a ~20% slowdown in netns creation:

[root@wsfd-netdev89 ~]# time for i in

; do ip netns add a; ip netns del a ; done

real 0m19,939s
user 0m0,830s
sys 0m2,807s

then I unloaded all IB modules and:
[root@wsfd-netdev89 ~]# time for i in

; do ip netns add a; ip netns del a ; done

real 0m19,818s
user 0m0,770s
sys 0m2,862s

These tests done while dumping tc filters with stats in parallel.

Perf record gives:

• 67,11% 0,16% ip [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe◆
  66,95% entry_SYSCALL_64_after_hwframe ▒
• do_syscall_64 ▒
• 56,44% __x64_sys_unshare ▒
  ksys_unshare ▒
  unshare_nsproxy_namespaces ▒
  create_new_namespaces ▒
  copy_net_ns ▒
  setup_net ▒
• ops_init ▒
• 32,50% rdma_dev_init_net ▒
  ^^^^^^
• add_one_compat_dev.part.25 ▒
• 30,25% ib_setup_port_attrs ▒
• 24,12% internal_create_groups.part.4 ▒
• internal_create_group ▒
• 23,51% sysfs_add_file_mode_ns ▒
• __kernfs_create_file ▒
• 18,02% kernfs_new_node ▒
• 17,80% __kernfs_new_node ▒
  + 10,41% kmem_cache_alloc ▒
  + 2,70% idr_alloc_cyclic ▒
  + 2,05% kstrdup ▒
  + 1,44% security_kernfs_init_security ▒
  + 4,52% kernfs_add_one ▒
  + 2,74% alloc_port_table_group.isra.3 ▒
• 1,46% ib_query_port ▒
  + 0,81% mlx5_ib_query_port ▒
  hw getting queried --------^^^^^^
  + 0,64% mlx5_query_port_roce ▒
  + 1,07% kobject_add ▒
  + 2,25% device_add ▒
  + 8,31% ip_tunnel_init_net ▒
  + 2,70% tcp_sk_init ▒
  + 2,42% loopback_net_init ▒
  + 1,91% inet6_net_init ▒
  + 1,49% icmpv6_sk_init ▒
  + 1,25% icmp_sk_init ▒
  + 1,08% nf_conntrack_pernet_init ▒
  + 1,04% ipv4_mib_init_net ▒
  0,66% sunrpc_init_net ▒
  + 2,02% __x64_sys_mount ▒
  + 1,86% __x64_sys_exit_group ▒
  + 1,77% ksys_mmap_pgoff ▒
  + 1,34% __x64_sys_mprotect ▒
  + 1,27% __x64_sys_execve ▒

Version-Release number of selected component (if applicable):
4.18.0-414.el8.x86_64

How reproducible:
Always

Steps to Reproduce:
1.blacklist mlx5_ib
2.reboot
3.test how long it takes to create 1000 netns
4.load mlx5_ib
5.test how long it takes to create 1000 netns again

Actual results:
Considerable slowness detected, about 20%.

Expected results:
Less of a impact, for a subsystem that is not being used on this host.

Additional info: