latencytap.stp - Show Reasons and Durations for Processes Sleeping

  The latencytap.stp script collects data on the intervals processes
  are deactivated (sleeping).  The script categorizes the reasons for
  the sleeps by analyzing the backtraces and displays a sorted list of
  the top 20 causes from largest total sum time sleeping to smallest.
  The output is updated every 30 seconds. The script needs to be
  compiled with the '--all-modules' option to produce reasons for
  sleeps caused by modules.  Optionally, this script can be used with
  the '-c' or '-x' options to focus on a specific PID.


$ stap latencytap.stp --all-modules -w

Reason                                            Count  Average(us)  Maximum(us) Percent%
kernel workqueue thread                             109      1232008     14462131      44%
Waiting for event (poll)                              3     13340013     20020024      13%
Waiting for event (poll)                            148       200224       200381       9%
RCU grace period kernel thread                        7      4010912      9997792       9%
                                                      5      5615087      9997712       9%

jdb2() kernel thread                                  2     10716824     14449748       7%
Application requested delay                           2      9999829      9999833       6%
jdb2() kernel thread                                  3       288906       541672       0%
RCU grace period kernel thread                        8         2542         2994       0%
                                                      7         2519         2958       0%
Creating block layer request                          1         1599         1599       0%
Submitting block IO                                  15          103          118       0%
jdb2() kernel thread                                  3          333          395       0%
Waiting for event (epoll)                             1          342          342       0%
Creating block layer request                          1          271          271       0%