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HelpMacOS.txt
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Version 2.5
This program implements a network response time and throughput test.
The program can be run as either a client or a server. The client opens one
or more connections to a server and exchanges messages of a given size with
the server for a given period of time. At the end of the test period, various
performance metrics are displayed.
The test can run in two modes. In synchronous (request/response) mode, each
connection has a single thread in both the client and the server. Once the
connection is established the client sends a message to the server and waits
for a response. As soon as the server receives a message it sends it straight
back to the client. This sequence is repeated until the test ends.
In asynchronous (streaming) mode, each connection has two threads in both the
client and the server. Once the connection is established the client sends a
continuous stream of messages to the server and the server simultaneously
sends a continuous stream of messages to the client.
The size of the messages exchanged, the duration of the test measurement phase,
the amount of load ramp-up and ramp-down time and the number of connections
(and hence threads) are all configurable.
The defaults for the various configurable parameters have been carefully chosen
such that using the defaults will generally give a meaningful result. The main
parameters that you might vary in normal usage are the message size and the
number of connections.
Usage:
nwtest h[elp] { h[elp] | i[nfo] | u[sage] | g[eneral] |
c[lient] | s[erver] | m[etrics] | f[ull] }
nwtest i[nfo]
nwtest s[erver] <port> [-4|-6] [-h[ost] <h>] [-m[sgsz] <m>]
[-c[onn] <c>] [-l[og] <logpath>]
nwtest c[lient] <host> <port> [-s[rc] <srcaddr>] [-4|-6] [-a[sync]]
[-c[onn] <c>] [-d[ur] <d>] [-r[amp] <r>]
[-m[sgsz] <m>] [-l[og] <logpath>] [-e[cn]|-noe[cn]]
[-sbsz <sbsz> | [[-srvsbsz <srvsbsz>] [-cltsbsz <cltsbsz>]]
[-rbsz <rbsz> | [[-srvrbsz <srvrbsz>] [-cltrbsz <cltrbsz>]]
[-n[odelay]] [-q[uickack]] [-b[rief]|-v[erbose]]
nwtest h[elp] { u[sage] | g[eneral] | c[lient] | s[erver] | m[etrics] | f[ull] }
Display help on the specified topic.
nwtest i[nfo] }
Display information about this utility.
nwtest s[erver] <port> [-4|-6] [-h[ost] <h>] [-m[sgsz] <m>]
[-c[onn] <c>] [-l[og] <logpath>]
Run as a server on local port <port>. If a specific host is specified (<h>)
then bind to the address(es) for that host, otherwise bind to INADDR[6]_ANY.
The host can be specified as a hostname or an IP address (IPv4 or IPv6);
the address specified must be an address for an interface on the local system.
If a hostname is specified then you can use the '-4' or '-6' options to limit
communication to IPv4 or IPv6.
The maximum message size, in bytes, that the server will accept is specified
by <m> where 28 <= <m> <= 1,048,576. Connections requesting a message size
larger than this will be rejected. The default is 1,048,576. This size
represents the size of the user data; it excludes network protocol overheads
(ethernet, IPv4/6 etc.). The size may be specified using a suffix of 'k' to
repesent KB (1,024 bytes) or 'm' to represent MB (1,048,576 bytes).
The maximum number of concurrent connections that the server will allow is set
using <c> where 2 <= <c> <= 128. Connections that exceed this number will
be rejected. The default is 32.
Normally all output goes to stdout/stderr, but if '-log' is specified then
after initial argument parsing any subsequent messages will be written only
to <logpath> with microsecond resolution timestamps. A <logpath> of '-'
equates to 'stdout' and '--' equates to 'stderr'.
nwtest c[lient] <host> <port> [-s[rc] <srcaddr>] [-4|-6] [-a[sync]]
[-c[onn] <c>] [-d[ur] <d>] [-r[amp] <r>]
[-m[sgsz] <m>] [-l[og] <logpath>] [-e[cn]|-noe[cn]]
[-sbsz <sbsz> | [[-srvsbsz <srvsbsz>] [-cltsbsz <cltsbsz>]]
[-rbsz <rbsz> | [[-srvrbsz <srvrbsz>] [-cltrbsz <cltrbsz>]]
[-n[odelay]] [-q[uickack]] [-b[rief]|-v[erbose]]
Run as a client connecting to a server at host <host> and port <port>. The
host can be specified as either a host name or an IP address (IPv4 or IPv6).
If a hostname is specified then you can use the '-4' or '-6' options to limit
communication to IPv4 or IPv6.
Normally the OS will determine the local source IP address (interface) to use
for the outgoing connection, but this can be overridden by specifying an
explicit local address using the '-src' option. This value must be an IP
address, not a hostname, and it must correspond to the address of an
interface on the local system. If <host> has been specified using an IP
address then the address type (IPv4 or IPv6) for <srcaddr> must be the same
as that of <host>. Furthermore, if the allowed connection type has been
restricted by way of '-4' or '-6' then the value of <srcaddr> must be of
the selected type.
By default the test is performed in request/response (synchronous) mode but
if '-async' is specified the test is performed in streaming mode.
The measurement part of the test will run for <d> seconds with a ramp-up/down
of <r> seconds. 10 <= <d> <= 300 with a default of 30 and 0 <= <r> <= 30
with a default of 10.
The message size used for the test is specified by <m> where 28 <= <m> <=
1,048,576 with a default of 1,024. This size represents the size of the user
data; it excludes network protocol overheads (ethernet, IPv4/6 etc.). The
size may be specified using a suffix of 'k' to repesent KB (1,024 bytes) or
'm' to represent MB (1,048,576 bytes).
The number of concurrent connections used is specified by <c> where 1 <= <c>
<= 64 with a default of 1.
Normally all output goes to stdout/stderr, but if '-log' is specified then
after initial argument parsing any subsequent messages will be written only
to <logpath> with microsecond resolution timestamps. A <logpath> of '-'
equates to 'stdout' and '--' equates to 'stderr'.
If you specify '-ecn', Explicit Congestion Notification is requested for
the connection. The system will attempt to negotiate ECN but there is no
guarantee that it will succeed and no indication if the negotiation fails.
If you specify '-noecn', Explicit Congestion Notification is disabled for
the connection.
Normally the OS will allocate the sizes for the socket send and receive
buffers, and these sizes will be reported in the connection messages. If
you want to use specific values for the socket send and receive buffer
sizes then you can do so using '-sbsz' (sets size for send buffer on both
client and server), '-rbsz' (sets size for the receive buffer on both client
and server), '-srvsbsz' (sets size for send buffer on server), '-srvrbsz'
(sets size for receive buffer on server), '-cltsbsz' (sets size for send
buffer on client) and '-cltrbsz' (sets size for receive buffer on client).
These values are specified in bytes and each must be between 4,096 and
4,194,304. Also, the total of the sizes must be <= 4,194,304. These sizes may
be specified using a suffix of 'k' to repesent KB (1,024 bytes) or 'm' to
represent MB (1,048,576 bytes).
Other factors, such as OS configuration, may place further constraints on
the maximum allowed send and receive buffer sizes. Use 'nwtest info' to
get more specific information.
If '-nodelay' is specified then the TCP_NODELAY option is enabled on all
sockets used for data transfer in both the client and the server.
If '-quickack' is specified then the TCP_SENDMOREACKS option is enabled on
all sockets used for data transfer in both the client and the server.
Normally only aggregate performance metrics are displayed, but if '-verbose'
is specified then per connection metrics are also displayed. If '-brief' is
specified then just key metrics are displayed on a single line.
For each connection successfully established, the client and server will
report the TCP MSS (maxseg) value and the size of the socket send and
receive buffers (sndbsz anb rcvbsz).
The metrics measured and reported by this program for each test mode are
as follows; all references to 'data' and 'throughput' refer to application
data excluding network overheads.
All modes
---------
Elapsed time - The wall clock elapsed time for the measurement part
of the test (excludes ramp up/down time).
User CPU time - The amount of user CPU time consumed during the
elapsed time.
System CPU time - The amount of system CPU time consumed during the
elapsed time.
Total CPU time - User time plus system time.
Process CPU usage - The average CPU usage for the nwtest process during
the elapsed time, expressed as a percentage of one
CPU core.
System CPU usage - The average CPU usage for the nwtest process during
the elapsed time, expressed as a percentage of total
available system CPU resources.
Sync (request/response) mode
----------------------------
Total messages - The total number of data messages sent during the
measurement period. The number of received messages
is the same.
Total data - The total number of bytes sent during the measurement
period. The number of received bytes is the same.
Avg measure time - The average measurement time across all threads (µs).
Start variance - The maximum difference between the start times of all
the threads (µs). Only displayed if connections > 1.
Run variance - The maximum difference between the measurement times of
all the threads (µs). Only displayed if connections > 1.
Throughput - The send throughput, aggregated across all connections,
during the measurement period (bytes/second).
Minimum R/T - The lowest round trip time across all connections during
the measurement period (µs).
Average R/T - The average round trip time across all connections during
the measurement period (µs).
Maximum R/T - The highest round trip time across all connections during
the measurement period (µs).
In brief mode the output consists of a single line as follows:
info: results S,<nconn>,<throughput>,<minrt>,<avgrt>,<maxrt>,<proccpu>,<syscpu>
Async (streaming) mode
----------------------
Total msg sent - The total number of messages sent during the measurement
period.
Total msg rcvd - The total number of messages received during the
measurement period.
Total data sent - The total number of bytes sent during the measurement
period.
Total data rcvd - The total number of bytes received during the measurement
period.
Avg measure time - The average measurement time across all threads (µs).
Start variance - The maximum difference between the start times of all
the threads (µs).
Run variance - The maximum difference between the measurement times of
all the threads (µs).
Send throughput - The send throughput, aggregated across all connections,
during the measurement period (bytes/second).
Recv throughput - The receive throughput, aggregated across all connections,
during the measurement period (bytes/second).
Average throughput - The average of the send and receive throughputs.
In brief mode the output consists of a single line as follows:
info: results A,<nconn>,<sendthroughput>,<recvthroughput>,<proccpu>,<syscpu>
Network overheads
-----------------
The message size that you specify defines the size of the 'application data'
in each message sent or received. The actual amount of data for each message
will be larger than this due to various network and protocol related overheads.
For IPv4/TCP, there is at least 28 bytes of overhead per message and in unusual
cases this may be as much as 36 bytes. In addition the TCPv4 header is another
24 bytes. In most cases, for this program, the IPv4 packet size will be <message
size> + 52 bytes.
For IPv6/TCP, there is at least 72 bytes of overhead per message and in unusual
cases this may be more due to additional header fields (each is 8 bytes). In
most cases, for this program, the IPv6 packet size will be <message size> + 72
bytes.
For Ethernet the standard Maximum Transmission Unit (MTU) is 1500 bytes. Each
IP packet will be sent as a sequence of one or more Ethernet frames. Each frame
has some overhead; normally this is 38 bytes but if 802.1q VLANs are being used
it will be 42 bytes.
For WiFi the standard Maximum Transmission Unit (MTU) is 1500 bytes. Each IP
packet will be sent as a sequence of one or more WiFi frames. Each frame has
some overhead; normally this is 36 bytes but it may be as much as 44 bytes.
To give this some context, with the default test message size of 1024 bytes the
IPv4 packet size will be 1076 bytes and the IPv6 packet size will be 1096 bytes.
Both will therefore fit into a single Ethernet/WiFi frame. The associated
Ethernet frame will be 1114 bytes for IPv4 and 1134 bytes for IPv6.
With a 1 Gbit/s Ethernet network, the maximum theoretical throughput will be
112,208 frames/s for IPv4 and 110,229 frames/s for IPv6. This translates to
a theoretical maximum application data rate of 109.5 Mbyte/s for IPv4 and
107.6 Mbyte/s for IPv6.