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.
Dialog is shown
by selecting the PVM Options item in the
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
- 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
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.
When a computer named is entered in the Host field,
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.
- List the machines in the PVM configuration.
- List the current PVM processes.
- 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 the changes made in the dialog.
- Dismiss the dialog without applying any changes or
undoing any that were previously applied.
PVM properties can also be set with the