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:
pollselectepollitimerfutexnanosleepsignal
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
--------------------------------------------------------------
