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REMRT(1)			    BRL-CAD			      REMRT(1)

NAME
       remrt - network distributed (remote) ray-trace dispatcher

SYNOPSIS
       remrt [options...] model.g objects...

DESCRIPTION
       remrt is	intended to be an entirely plug-compatible replacement for the
       rt(1) program. While rt can operate on more than	one processor of a
       shared memory MIMD style	multi-processor, it can	not spread the work
       out across the network.	remrt and its companion	program	rtsrv(1)
       implement a libpkg(3)-based protocol for	distributing the task of
       ray-traced rendering out	to an arbitrary	number of processors on	the
       network.	Those processors can be	from an	arbitrary mix of vendors, with
       differing instruction sets and data representations, operating at
       widely different	speeds.

       remrt provides two levels of fault-tolerance in its distributed
       computation. First, any rtsrv processor which fails (or whose network
       link fails) will	have its work reassigned automatically by remrt	to
       other processors, so that the failure of	that processor does not	hold
       up the progress of the computation. On a	regular	interval remrt
       attempts	to restart computation on failed processors marked "active",
       so that when failed systems become available again they are put back to
       work. Second, remrt offers a form of "checkpoint-restart" by carefully
       writing all received pixel data immediately to disk. If the machine
       running remrt should fail, when remrt is	restarted, it will determine
       what work remains to be done and	restart	all the	rtsrv processes	on the
       remote machines.

       remrt takes exactly the same set	of command line	arguments as rt(1).
       For a full discussion of	those options, consult the rt(1) manual	page.
       From within mged(1) the remrt program can be run	from the current mged
       view by giving the mged command

		rrt remrt -M -s###

       where "###" is the image	resolution desired.

       remrt depends on	the Berkeley rsh (1) remote shell command and the
       user's corresponding ".rhosts" file to automatically initiate remote
       computation.

       remrt requires a	control	file called ".remrtrc" which specifies a few
       essential parameters of the server machines (network hosts) that	are to
       participate in the distributed computation. The ".remrtrc" file
       contains	a list of normal remrt commands	which are to be	executed
       before distributed processing is	to begin. This can be useful for
       establishing a variety of user-specific defaults. However, the most
       important command to provide is a "host"	command	to describe each of
       the remote hosts	that will (or may) participate in the distributed
       computation. Here is a sample ".remrt" file:

	   host	wolf passive cd	/tmp/cad/.remrt.4d
	   host	voyage	  always cd /tmp/cad/.remrt.4d
	   host	whiz hacknight convert /tmp

       The first argument to the "host"	command	is the name of the server
       machine.	It will	be converted to	a fully	qualified name by calling
       gethostbyname(3)	and gethostbyaddr(3).

       The second argument to the "host" command describes "when" this machine
       should be used.

       always
	   says	that whenever this host	is not participating in	the
	   computation,	repeated attempts should be made (every	5 minutes) to
	   start an rtsrv process on that machine. This	option is most useful
	   for machines	where the system administrator and/or owner of the
	   machine won't mind your using the machine at	any time. (Note	that
	   rtsrv runs at the lowest priority by	default, so this isn't too
	   terribly uncivilized. But be	polite and ask first.)

       night
	   indicates that the machine should only be used during the night and
	   on weekends.	Night extends from 1800	through	0000 to	0800. Saturday
	   and Sunday are considered to	be in night time for the entire	day.

       hacknight
	   indicates that the machine is owned by a late-night "hacker", and
	   can be used while that hacker is likely to be asleep. Hacking tends
	   to run from 1300 through 0000 to 0400, so hacknight is the time
	   period from 0400 to 1300.

       passive
	   indicates that remrt	should never attempt to	initiate an rtsrv
	   process on this machine, but	if the user should happen to start
	   rtsrv manually on the machine and direct it to join the
	   computational fray, then the	necessary information will be
	   available.

       If an unlisted machine should join the fray, it will be added
	   with	a "when" value of passive and a	"where"	value of convert. When
	   an rtsrv passes from	night into day,	it is automatically terminated
	   by remrt at the appointed time.

       The third argument to the "host"	command	is the "where" parameter,
       which indicates where the BRL-CAD ".g" file (and	any related texture
       maps) can be found.

       cd
	   indicates that the rtsrv program should change directory cd(2) to
	   the indicated directory path, and should just read the data files
	   in that directory as	rt normally would. This	can be used to specify
	   NFS or RFS mounted remote directories, or static copies of the
	   binary database file(s) needed to perform the ray-tracing. This is
	   the most efficient way of operating rtsrv, but it also requires
	   some	manual preparation on the part of the user to install all the
	   required files in the designated location.

       convert
	   indicates that remrt	should send across an ASCII
	   machine-independent version of the ".g" database file using the
	   command:

		   asc2g < file.g | rsh	host 'cd directory; g2asc > file.g'

	   before starting up the rtsrv	program	in that	same directory.	This
	   relieves the	user of	the burden of setting up the ".g" database
	   file, but suffers from several drawbacks. First, the	transmission
	   of a	large database can take	a noticeable amount of time. Second,
	   should the server host go down and then re-join the fray, the
	   database will be sent again,	because	remrt has no easy way to tell
	   if the previous ".g"	file is	still intact after the crash/restart.
	   Third, remrt	has no way to tell what	auxiliary files	might be
	   needed for this ".g"	file, and thus can not send them
	   automatically. If the ".g" file references height field, extruded
	   bit-map, or volumetric solids, the associated data files will not
	   be present on a convert mode	server.	The same applies for texture
	   map and bump	map files.

       remrt uses several different strategies for optimizing the dispatching
       of work.	These can be controlled	by the "allocate" command. If
       "allocate frame"	has been specified, then the work allocation method is
       a "free for all", allocating work from one frame	at a time to all
       servers as they become ready for	more. This maximizes the CPU overhead
       for prepping (because all CPUs will prep	all frames), but it also
       provides	the shortest wall-clock	time to	getting	the first frame
       finished. This mode is recommended for demonstrations, and other
       situations where	people are sitting around waiting for results to
       appear on the screen.

       If the "allocate	load" command has been given, then new servers will
       not be assigned to a given frame	unless there is	at least enough	work
       remaining on that frame to require 10 percent of	that server's measured
       performance capacity. Otherwise the server is started on	a subsequent
       frame.

       If the "allocate	movie" command is given, then each server is allocated
       a whole frame to	do. This minimizes the CPU time	spent in the overhead
       of prepping the frame, and tends	to maximize overall throughput,	at the
       price of	making you wait	a long time for	the first frame	to finish.
       This mode is best used when crunching out large numbers of frames for
       an animation. (See also the scriptsort(1) command for a clever
       power-of-two script rearrangement technique first proposed by Jim
       Blinn).

       The output can be stored	either in a file, or sent to the current
       framebuffer, the	same as	with rt(1).

       When remrt is run without command line arguments, it enters an
       interactive mode. In this mode, the current framebuffer can be assigned
       and released, frames can	be added to the	list of	pending	work, and many
       other control and status	commands can be	used.

       Normally	remrt runs in a	batch mode, taking all its information from
       the command line, the script file on stdin, and the ".remrtrc" file. If
       you wish	to issue an interactive-style command to remrt while it	is
       running in batch	mode, this can be accomplished by giving an extra
       argument	to rtsrv, which	will simply pass on the	command	and exit. For
       example:

	       rtsrv server_host 4446 status

       would send the command "status" to the remrt process running on the
       machine called "server_host" and	listening at port 4446.	4446 is	the
       port used by the	first copy of remrt running on a machine. If a second
       copy of remrt is	started	while the first	one continues to run, it will
       be assigned port	4447. One is added to the port number repeatedly until
       an available port is found. Normally you	do not need to worry about
       which port is being used, unless	you wish to send commands there
       directly. The netstat(1)	command	can sometimes be useful	to track down
       which ports are being used.

SEE ALSO
       rtsrv(1), rt(1),	scriptsort(1), brlcad(1), mged(1), lgt(1), pix-fb(1),
       rtray(1), rtpp(1), librt(3), ray(5V), pix(5)

DIAGNOSTICS
       Numerous	error conditions are possible. Descriptive messages are
       printed on standard error.

SEE ALSO
       M. Muuss, "Workstations,	Networking, Distributed	Graphics, and Parallel
       Processing", in "Computer Graphics Techniques: Theory and Practice",
       ed: Rogers & Earnshaw, Springer Verlag, New York, pages 409-472

BUGS
       Most deficiencies observed while	using the remrt	program	are usually
       with the	rt(1) program, with which it shares a substantial amount of
       common code, or with the	librt(3) library. If a frame fails to render
       properly, try processing	it on a	single machine using rt(1) to
       determine if the	problem	is in the ray-tracing side of things, or the
       distributed computation side of things.

AUTHOR
       BRL-CAD Team

COPYRIGHT
       This software is	Copyright (c) 1994-2019	by the United States
       Government as represented by U.S. Army Research Laboratory.

BUG REPORTS
       Reports of bugs or problems should be submitted via electronic mail to
       devs@brlcad.org

BRL-CAD				  08/29/2020			      REMRT(1)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | DIAGNOSTICS | SEE ALSO | BUGS | AUTHOR | COPYRIGHT | BUG REPORTS

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