gethostlatency(8)

NAME
gethostlatency - Show latency for getaddrinfo/gethostbyname[2] calls. Uses Linux eBPF/bcc.

SYNOPSIS
gethostlatency

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.

REQUIREMENTS
CONFIG_BPF and bcc.

OPTIONS

-p PID
    Trace this process ID only.

EXAMPLES

Trace host lookups (getaddrinfo/gethostbyname[2]) system wide:
    # gethostlatency

FIELDS

TIME
    Time of the command (HH:MM:SS).

PID Process ID of the client performing the call.

COMM
    Process (command) name of the client performing the call.

HOST
    Host name string: the target of the lookup.

OVERHEAD
The rate of lookups should be relatively low, so the overhead is not expected to be a problem.

SOURCE
This is from bcc.

    https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS
Linux

STABILITY
Unstable - in development.

AUTHOR
Brendan Gregg

SEE ALSO
tcpdump(8)