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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, int msg_size, attr_list attrs)
long CMprobe_bandwidth (CMConnection conn, int 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,
int    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.

long CMprobe_bandwidth (  CMConnection    conn,
int    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 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.

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