.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 4.4 feature (bpf_perf_event_output());
for kernels older than 4.4, 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)