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PVM


The optional PVM (Parallel Virtual Machine) version of Sabrina permits Sabrina's ray tracing to be carried out on multiple computers simultaneously.

The PVM mode is in effect, and multiple computers will be used if so configured, if the PVM item in the Options menu is checked.

The PVM Dialog is shown by selecting the PVM Options item in the Options menu. The dialog contains a check box for enabling the PVM mode and controls for defining the configuration and setting options.

PVM Enabled
Sabrina will use the Parallel Virtual Machine if the box is checked. Otherwise, Sabrina will execute only on the local computer.
 
Slave With Master
When checked, a slave process will run on the master computer. The master computer is usually the local computer. The slave processes perform the ray tracing calculations. If PVM is enabled and Slave with Master is unchecked, checking it will start the new slave at once. Disabling the mode does not make the slave go away---PVM must be disabled and then enabled. Because the slave process competes with the master's work of displaying the grpahics, the advantage of running the slave on the master's processor depends on the relative speed of the computers in the configuration.
Display Bars
When checked, a bar code along the left side of the graphics window shows which slave computed each band in the picture. Each band has a series of lights representing the binary code for the number of the slave that processed the bad. The binary code is evaluated from left to right, so that the positions of the lights represent 1 2 4 8 16. The codes give an indication of whether the work is being shared equally or if one or a few computers dominate.

Host
When a computer named is entered in the Host field, selecting Add will include that machine in the PVM configuration and cause a slave to be run on that machine if the add is successful. Delete removes the computer from the PVM configuration.

Loop Delay
The master and distributor processes continuously check for data and messages from the slaves while picture is being made. This polling can take a significant amount of time, especially on fast computers. If a query found no message waiting, the processes wait for Loop Delay milliseconds before querying again. The delay must be less than 1 second and greater than or equal to 1 millisecond. The optimum value depends on the PVM configuration and the complexity of the picture.

Slave Nice Value
Slaves on Unix computers will be run with the specified nice value. The value should be between 1 (high priority) and 20 (low priority). The value has no effect on slaves run on Windows computers.

Conf
List the machines in the PVM configuration.

Ps
List the current PVM processes.

Stats
List statistics for the last picture, including how many bands were contributed by each computer and their time per band. For Unix computers, both processing and system times are given.

Host File
Show the file selection dialog in which to choose the PVM host file. The file contains a list of hosts that Sabrina will add to the PVM configuration when Sabrina starts PVM. The file is not used if PVM is already running when Sabrina starts.

Apply
Apply the changes made in the dialog.

Dismiss
Dismiss the dialog without applying any changes or undoing any that were previously applied.

PVM properties can also be set with the PVM commands.