108 lines
5 KiB
Text
108 lines
5 KiB
Text
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GENERAL INFORMATION:
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This code computes the equilibrium distribution of light in a scene
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using the hierarchical diffuse radiosity method. A description of the
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sequential hierarchical radiosity method can be found in
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Pat Hanrahan, David Salzman and Larry Aupperle, "A Rapid Hierarchical
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Radiosity Algorithm", Proc. SIGGRAPH 1991.
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Descriptions of the parallel algorithm can be found in
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Jaswinder Pal Singh, Anoop Gupta and Marc Levoy, "Parallel
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Visualization Algorithms: Performance and Architectural Implications",
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IEEE Computer, July 1994.
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or in
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Jaswinder Pal Singh, et al, "Load Balancing and Data Locality in
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Hierarchical N-body Methods", Stanford Univ. Tech Report CSL-TR-92-505
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(to appear in JPDC).
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A detailed description will also be in the SPLASH-2 report.
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The parallelism is managed with distributed task queues and task
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stealing, and there is one task queue per processor.
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RUNNING THE PROGRAM:
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To see how to run the program, please see the comment at the top
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of the main.C file or run it as "RADIOSITY -h". Many of the
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command-line options control the accuracy of the program's computation
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and have default values set in the program (which can be overridden by
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command-line specifications). These are indicated as such in the
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comments or usage statement, and we recommend that they be left at
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their default values for base SPLASH-2 runs.
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The program runs in different modes, either interactive (using the SGI
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GL library) or batch. The batch mode does not attempt to display the
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rendered image, while the interactive mode brings up a GL window with
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knobs and dials to set parameters and run the program. If you are
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running on a system that does not support GL or you do not want to
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display the resulting scene, please use the -batch option on the
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command line. The makefile shows you how to link the GL libraries.
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This sample makefile is for a machine on which we do not want to
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display, in which case we use the glibdumb and glibps libraries, which
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do not support displaying and are provided with the code. The only
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real way to verify the correctness of the program is to view the
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result using GL. The commented lines in the print_statistics routine
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can be uncommented to print several runtime statistics, but these are
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nondeterministic in parallel since the program does not follow a
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deterministic execution path and does not arrive at exactly the same
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result in different parallel runs (the radiosity algorithm is
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iterative to convergence, and even the path is nondeterministic).
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The way the program is written, it compiles in the input description
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of the scene in polygon coordinates. This is in the file room_model.C,
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which contains the descriptions of two scenes. One is the room scene
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originally used by Hanrahan et al in their SIGGRAPH paper, and the
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other is an artificial extension of this scene (removing a wall of the
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room and introducing some of the features of this room in the
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neighboring room thus created). To use the former, use the -room
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command line option; for the latter, use -largeroom. -room is what we
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call the base SPLASH problem. If you don't specify -room or
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-largeroom, the program will default to a small dummy test scene which
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is useful only for debugging the program and verifying that it works.
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There are two types of compile-time flags that can be set in the code.
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One controls the manner in which patches are assigned to processors at
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the beginning of each time-step in the radiosity iteration. The simple
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case is to assign the same statically chosen set of patches to the
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same processor in every iteration (and rely completely on task
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stealing for load balancing); this is what happens by default, or if
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-DPATCH_ASSIGNMENT_STATIC is used as a compile-time flag. The more
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sophisticated case is to do an assignment at the beginning of a time
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step based on the costs of patches profiled in the previous time step;
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this is what happens if the -DPATCH_ASSIGNMENT_COSTBASED flag is used
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at compile-time. The latter can yield less stealing, but uses more
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synchronization to keep track of costs and hence has more overhead.
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We recommend using the default (not defining anything, so static is
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used) in the base SPLASH runs.
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The other type of compile-time flag special cases some machines in
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terms of maximum number of processors etc. (grep for #if in *.C and
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*.H to find these) and even memory consistency model in one instance.
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BASE PROBLEM SIZE:
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The base problem size we recommend is to use the program as follows:
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RADIOSITY -p ? -batch -room
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where ? is the number of processors. This sets the ae, bf etc flags
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(see comment at top of rad_main.C or run "RADIOSITY -h" to see what
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these are) to their default values. The default values can be found
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by looking at the comment at the top of rad_main.C or running
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"RADIOSITY -h".
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DATA DISTRIBUTION:
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Data distribution is very difficult in this code, except for some
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per-process data structures (typically arrays of structures indexed by
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process_id; grep for MAX_PROCESSORS to find them).
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General data distribution of other (scene, e.g.), however, does not
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make much difference to performance on the Stanford DASH
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multiprocessor.
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