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