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

AUTHOR¶

Brendan Gregg

SEE ALSO¶

tcpdump(8)