$ perf top -C 32
34.37% [kernel] [k] do_select
32.10% [kernel] [k] __fget_light
18.89% [kernel] [k] fput_many
3.42% [kernel] [k] __x86_return_thunk
1.42% [kernel] [k] __fdget
1.41% [kernel] [k] fput
0.89% [kernel] [k] memset_erms
0.75% [kernel] [k] copy_user_enhanced_fast_string
0.54% [kernel] [k] read_tsc