4.3.5. Tracking Most Frequently Used System Calls

timeout.stp from Section 4.3.4, “Monitoring Polling Applications” helps you identify which applications are polling by pointing out which ones used the following system calls most frequently:
  • poll
  • select
  • epoll
  • itimer
  • futex
  • nanosleep
  • signal
However, in some systems, a different system call might be responsible for excessive polling. If you suspect that a polling application is using a different system call to poll, you need to identify first the top system calls used by the system. To do this, use topsys.stp.
topsys.stp

#! /usr/bin/env stap
#
# This script continuously lists the top 20 systemcalls in the interval 
# 5 seconds
#

global syscalls_count

probe syscall.* {
  syscalls_count[name]++
}

function print_systop () {
  printf ("%25s %10s\n", "SYSCALL", "COUNT")
  foreach (syscall in syscalls_count- limit 20) {
    printf("%25s %10d\n", syscall, syscalls_count[syscall])
  }
  delete syscalls_count
}

probe timer.s(5) {
  print_systop ()
  printf("--------------------------------------------------------------\n")
}

topsys.stp lists the top 20 system calls used by the system per 5-second interval. It also lists how many times each system call was used during that period. Refer to Example 4.15, “topsys.stp Sample Output” for a sample output.

Example 4.15. topsys.stp Sample Output

--------------------------------------------------------------
                  SYSCALL      COUNT
             gettimeofday       1857
                     read       1821
                    ioctl       1568
                     poll       1033
                    close        638
                     open        503
                   select        455
                    write        391
                   writev        335
                    futex        303
                  recvmsg        251
                   socket        137
            clock_gettime        124
           rt_sigprocmask        121
                   sendto        120
                setitimer        106
                     stat         90
                     time         81
                sigreturn         72
                    fstat         66
--------------------------------------------------------------