Performance-query functions

These functions intrusively test the characteristics of a connection, measuring available bandwidth and current round-trip latency. More...

Functions
long	CMprobe_latency (CMConnection conn, long msg_size, attr_list attrs)
double	CMprobe_bandwidth (CMConnection conn, long size, attr_list attrs)
double	CMregressive_probe_bandwidth (CMConnection conn, long size, attr_list attrs)

Detailed Description

These functions intrusively test the characteristics of a connection, measuring available bandwidth and current round-trip latency.

Function Documentation

long CMprobe_latency	(	CMConnection	conn,
		long	msg_size,
		attr_list	attrs
	)

Probe the approximate round-trip latency on a particular connection by sending a burst of data.

This is an intrusive probe.

Parameters

conn	The CMConnection to be tested.
msg_size	The size of message to be sent in the test. (Latency varies dramatically with the message size.)
attrs	Currently this parameter is ignored, but it should allow control over the number of messages sent.

Returns

The return value is in units of microseconds.

Note

CM measures latency by sending a message and waiting for a response. This round-trip is called a "ping". In the current implementation, CM performs 2 ping operations to "warm up" the connection. It then performs 5 additional ping operations, measuring the time required for each. The return value is the average of these final operations.

double CMprobe_bandwidth	(	CMConnection	conn,
		long	size,
		attr_list	attrs
	)

Probe the available bandwidth on a particular connection by sending a burst of data.

This is an intrusive probe.

Parameters

conn	The CMConnection to be tested.
size	The size of message to be sent in the test. (Bandwidth varies dramatically with the message size.)
attrs	Currently this parameter is ignored, but it should allow control over the number of messages sent.

Returns

The return value is in units of MBytes per second.

Note

In the current implementation, CM sends messages to probe available bandwidth, where is calculated as . That is, CMprobe_bandwidth sends about 100Kbytes of data.

double CMregressive_probe_bandwidth	(	CMConnection	conn,
		long	size,
		attr_list	attrs
	)

Probe the available bandwidth on a particular connection by sending several streams and do a linear regression.

This is an intrusive probe.

Parameters

conn	The CMConnection to be tested.
size	The size of message to be sent in the test. (Bandwidth varies dramatically with the message size.)
attrs	Currently this parameter is ignored, but it should allow control over the number of messages sent.

Returns

The return value is in units of KBytes per second.

Note

In the current implementation, CM sends messages to probe available bandwidth, where is calculated as . That is, CMprobe_bandwidth sends about 100Kbytes of data.