| .TH gethostlatency 8 "2016-01-28" "USER COMMANDS" |
| .SH NAME |
| gethostlatency \- Show latency for getaddrinfo/gethostbyname[2] calls. Uses Linux eBPF/bcc. |
| .SH SYNOPSIS |
| .B gethostlatency |
| .SH DESCRIPTION |
| This traces and prints when getaddrinfo(), gethostbyname(), and gethostbyname2() |
| are called, system wide, and shows the responsible PID and command name, |
| latency of the call (duration) in milliseconds, and the host string. |
| |
| This tool can be useful for identifying DNS latency, by identifying which |
| remote host name lookups were slow, and by how much. |
| |
| This makes use of a Linux 4.5 feature (bpf_perf_event_output()); |
| for kernels older than 4.5, see the version under tools/old, |
| which uses an older mechanism |
| |
| This tool currently uses dynamic tracing of user-level functions and registers, |
| and may need modifications to match your software and processor architecture. |
| |
| Since this uses BPF, only the root user can use this tool. |
| .SH REQUIREMENTS |
| CONFIG_BPF and bcc. |
| .SH OPTIONS |
| .TP |
| \-p PID |
| Trace this process ID only. |
| .SH EXAMPLES |
| .TP |
| Trace host lookups (getaddrinfo/gethostbyname[2]) system wide: |
| # |
| .B gethostlatency |
| .SH FIELDS |
| .TP |
| TIME |
| Time of the command (HH:MM:SS). |
| .TP |
| PID |
| Process ID of the client performing the call. |
| .TP |
| COMM |
| Process (command) name of the client performing the call. |
| .TP |
| HOST |
| Host name string: the target of the lookup. |
| .SH OVERHEAD |
| The rate of lookups should be relatively low, so the overhead is not expected |
| to be a problem. |
| .SH SOURCE |
| This is from bcc. |
| .IP |
| https://github.com/iovisor/bcc |
| .PP |
| Also look in the bcc distribution for a companion _examples.txt file containing |
| example usage, output, and commentary for this tool. |
| .SH OS |
| Linux |
| .SH STABILITY |
| Unstable - in development. |
| .SH AUTHOR |
| Brendan Gregg |
| .SH SEE ALSO |
| tcpdump(8) |
