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tcpconnlat.8
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tcpconnlat.8
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.TH tcpconnlat 8 "2016-02-19" "USER COMMANDS"
.SH NAME
tcpconnlat \- Trace TCP active connection latency. Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B tcpconnlat [\-h] [\-t] [\-p PID] [-v] [min_ms]
.SH DESCRIPTION
This tool traces active TCP connections
(eg, via a connect() syscall), and shows the latency (time) for the connection
as measured locally: the time from SYN sent to the response packet.
This is a useful performance metric that typically spans kernel TCP/IP
processing and the network round trip time (not application runtime).
All connection attempts are traced, even if they ultimately fail (RST packet
in response).
This tool works by use of kernel dynamic tracing of TCP/IP functions, and will
need updating to match any changes to these functions. This tool should be
updated in the future to use static tracepoints, once they are available.
Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print usage message.
.TP
\-t
Include a timestamp column.
.TP
\-p PID
Trace this process ID only (filtered in-kernel).
.TP
\-v
Print the resulting BPF program, for debugging purposes.
.TP
min_ns
Minimum duration to trace, in milliseconds.
.SH EXAMPLES
.TP
Trace all active TCP connections, and show connection latency (SYN->response round trip):
#
.B tcpconnlat
.TP
Include timestamps:
#
.B tcpconnlat \-t
.TP
Trace PID 181 only:
#
.B tcpconnlat \-p 181
.TP
Trace connects with latency longer than 10 ms:
#
.B tcpconnlat 10
.TP
Print the BPF program:
#
.B tcpconnlat \-v
.SH FIELDS
.TP
TIME(s)
Time of the response packet, in seconds.
.TP
PID
Process ID that initiated the connection.
.TP
COMM
Process name that initiated the connection.
.TP
IP
IP address family (4 or 6).
.TP
SADDR
Source IP address.
.TP
DADDR
Destination IP address.
.TP
DPORT
Destination port
.TP
LAT(ms)
The time from when a TCP connect was issued (measured in-kernel) to when a
response packet was received for this connection (can be SYN,ACK, or RST, etc).
This time spans kernel to kernel latency, involving kernel TCP/IP processing
and the network round trip in between. This typically does not include
time spent by the application processing the new connection.
.SH OVERHEAD
This traces the kernel tcp_v[46]_connect functions and prints output for each
event. As the rate of this is generally expected to be low (< 1000/s), the
overhead is also expected to be negligible. If you have an application that
is calling a high rate of connects()s, such as a proxy server, then test and
understand this overhead before use.
.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
tcpconnect(8), tcpaccept(8), funccount(8), tcpdump(8)