CPU負荷が高い時、kworkerの負荷が高いときなど
細かな調査ができる。

http://nishitki.hatenablog.com/entry/2017/07/12/123715

# perf top
Samples: 368  of event 'cpu-clock', Event count (approx.): 71929660
Overhead  Shared Object       Symbol
   7.18%  [kernel]            [k] kallsyms_expand_symbol
   6.12%  libc-2.12.so        [.] __strstr_sse2
   5.59%  [kernel]            [k] memcpy
   5.59%  perf                [.] symbols__insert
   5.32%  libc-2.12.so        [.] memchr
   5.06%  [kernel]            [k] number
   4.26%  perf                [.] rb_next
   3.19%  [kernel]            [k] vsnprintf
   2.93%  [kernel]            [k] format_decode
・
・
・