SYNTAXxmpi [-h] [<boot_schema>]
DESCRIPTIONXMPI is a graphical user interface for running MPI programs, monitoring MPI processes and messages, and viewing execution trace files. It exploits the debugging capabilities of LAM, a parallel computing environment for UNIX clusters. XMPI is constructed from the Motif widget set.
XMPI does not provide an interface for starting a LAM session. This must be accomplished prior to running XMPI, which is itself a LAM program. The boot schema from which LAM was started can (should) be provided to XMPI so that it may be presented as an inventory of nodes on which programs may be run. If XMPI is to be used only to view trace files then starting LAM is not required.
This description assumes a basic knowledge of MPI.
TYPICAL USAGEXMPI provides a graphical display of the state of the processes within an MPI application. The state information is obtained from one of two sources, a running application started by XMPI or a file containing trace data from a traced MPI application. When XMPI is started, its top-level overview window is blank. Once an application is started or a trace file is loaded the overview window fills with a tiled group of hexagons, each representing the state of one MPI process and labeled by the process rank within MPI_COMM_WORLD. A traffic light symbol indicates whether the process is running or blocked. No traffic light is shown for processes which have either finalized or not yet initialized the MPI library.
When monitoring a running application the camera "Snap" button or "Snapshot" item in the "Application" menu updates the state information on all processes at any time. When viewing trace data the state information is updated according to the currently selected time point (see "XMPI TRACE FILES").
A mouse click inside a hexagon pops up an additional window containing more detailed information about the process. If the process is blocked, the function name, peer process rank, communicator, message tag and element count are displayed. If unreceived messages are available, their quantity, source process rank, communicator, message tag and element count are displayed. By leaving a few process windows on the screen, a user can focus debugging on a small and manageable collection of misbehaving processes.
The "Clean" button or "Clean" item in the "Application" menu terminates an application and the development cycle can be repeated. The previous application can be rerun with the "Rerun" button or "Rerun" item in the "Application" menu.
RUNNING AN APPLICATIONAn application schema specifies an MPI application by listing each process's program name, program location, target processor(s) and optional command line arguments.
The "Browse&Run" item in the "Application" menu pops up a simple file browser for choosing and running a pre-written application schema. Alternatively an application schema can be configured with the XMPI application builder dialog, invoked by the "Build&Run" item in the "Application" menu.
The builder dialog has an area to specify each process and an arrow button to add it to the application schema, which is shown below the arrow button in a scrolled list. The lines in the list show the syntax that would be used in creating the same application with a text editor. Indeed, the "Save" button saves the application schema in a file for later use and/or editing.
A specified process does not become part of the application until the arrow (commit) button is pressed. Once it appears in the application scrolled list, a process can be deleted by selecting it and pressing the <Delete> key.
Pressing the "Run" button with anything in the application list causes that application to be run. The overview window is then initialized with the status of the application.
Program SpecificationA file browser in the middle of the builder dialog aids in selecting a program file. The browser only navigates the file space of the node running XMPI. If a program is located on another node outside the file space (outside NFS, etc.) its pathname may need to be typed into the process specification area. Selecting the "Use Full Pathname" toggle button will cause programs to be placed into the application schema as full pathnames.
XMPI limits the choice of a program source node to either the node running XMPI or the process target node. The latter case is the default and is the most efficient because LAM does not need to transfer the program from source to target node. The "Transfer Program" toggle button selects the source node policy.
Multiple Program CopiesThe number of copies of a program to be run can be set in the process specification area. Clicking on the increment or decrement arrow will increment or decrement the count by one. Clicking with the shift key down will increment or decrement by ten.
Command-line ArgumentsCommand-line arguments must be typed into the process specification area.
Node SpecificationA boot schema specifies the computers participating as nodes in a LAM multicomputer. If XMPI is given a boot schema filename, its contents will appear in a scrolled list on the right side of the builder dialog. XMPI will search for the given schema in the local directory. The boot schema filename is displayed above the list of its nodes. Multiple target nodes can be selected from the scrolled list with the corresponding node mnemonic appearing in the process specification area. Selecting multiple target nodes specifies multiple processes with the program name, arguments and source node policy held constant.
If no boot schema was specified only the special node selectors "LOCAL" (meaning the node on which XMPI is running) and "ALL NODES" are provided.
Target node descriptions may also be typed directly into the process specification area. The local node is specified as h. The origin node from which the machine was booted, if not local, can be specified as o. All usable nodes are specified as N. Nodes are generically identified as n<list>, where <list> can be a single node identifier or a list of node identifiers. Identifiers can be written in decimal or hexadecimal notation. Examples are n1 or n0-7,0x10.
Run-time OptionsApplications can be run with various run-time options to specify the behaviour of the MPI library. These can be configured from a separate dialog which is activated from the "Runtime" item in the "Options" menu. Options remain in effect until changed.
- tracing mode (default enabled)
- fast client-to-client communication (default disabled)
- GER protocol and error detection (default enabled)
- homogeneous LAM node optimization (default disabled)
FOCUSING ON A PROCESSMore information on a process's state can be obtained by clicking the left mouse button within the process hexagon. This will pop up a focus window. The upper area of the focus window is the process area and displays the current state of the process. The lower area is the message area and displays information on the process's message queue.
The focus window banner contains a tack button which can be clicked to dismiss the window and a label containing the process's identity along with the program name. In XMPI processes are identified first by their rank in MPI_COMM_WORLD and if the process is communicating, with a slash followed by the process's rank within the current communicator. The focus window can also be dismissed by clicking once again in the process hexagon.
The process area describes the current state of the process together with the name of and (where appropriate) arguments to the MPI function currently being executed. The layout is fairly self-explanatory and we describe only the less obvious features.
Communicator IdentificationThe "comm" area shows the communicator being used in the current MPI function. Communicators are opaque objects which MPI does not identify in any meaningful, printable way. LAM's MPI implementation adds a simple numerical identifier to communicators, which is displayed in XMPI as <x> where x is the identifier. This identifier can be matched to communicator variables in an MPI program with the LAM function, MPIL_Comm_id(2).
Group MembershipThe button to the right of the "comm" area will highlight in the overview window the hexagons of the processes in the communicator. For an intracommunicator, the hexagons will be highlighted in the color specified by the "lcomCol" resource. For an intercommunicator, processes in the local group will be highlighted in the color specified by the "lcomCol" resource and those in the remote group in the color specified by the "rcomCol" resource. For highlighted processes the process identification at the bottom of the hexagon is changed to be the rank in MPI_COMM_WORLD followed by a slash and the rank in the communicator being highlighted.
DatatypeThe datatype button to the right of the "cnt" area will display in the datatype window (see "DATATYPE WINDOW") the type map of the datatype argument to the current MPI function.
The message area describes the current state of the queue of messages destined to the process and not yet received. Once again the layout is fairly self-explanatory and we describe only the less obvious features.
Message AggregatesIdentical undelivered messages are aggregated. The "copy" area shows the number of messages within the visible aggregate, followed by the total number of messages in the queue. The button to the right of the "copy" area cycles through the message aggregates.
Source RankThe "src" area shows the rank of the source process within MPI_COMM_WORLD followed by the rank of the source process in the communicator in which the message was sent.
DatatypeThe datatype button to the right of the "cnt" area will display in the datatype window the type map of the message's datatype.
Group MembershipThe button to the right of the "comm" area will highlight the message communicator in the manner previously described.
XMPI TRACE FILESXMPI can be used to view existing trace files and can be used to create trace files for applications run under XMPI.
To load and view an existing trace file select the "View" item in the "Trace" menu.
If an application is run under XMPI with tracing enabled (the default), LAM will trace the application. Before the trace data can be viewed in XMPI it must be dumped to a file. This is done by selecting the "Dump" item from the "Trace" menu. You will be prompted for a file name. By convention XMPI trace files have a ".lamtr" suffix. The trace file can be viewed by loading it as described above. As a shortcut select the "Express" item in the "Trace" menu, or equivalently click the "Trace" button in the overview window. This dumps the trace data to a temporary file and then immediately loads the file for viewing. If you decide that you want to save trace data for later viewing then you must dump it using the "Dump" item from the "Trace" menu. Dumping trace data to file does not purge any trace data and a subsequent dump will contain all the trace data from the start of the application up until the time of dumping. Terminating an application via the "Clean" button or menu item purges all trace data.
While viewing a trace an application previously launched by XMPI continues to run in the background. Upon the closing of the trace window XMPI will return to snapshot mode if there is a running application.
When loading trace files containing multiple segments (see MPIL_Trace_on(2) and MPIL_Trace_off(2)) you will be prompted for the number of the segment you wish to view. If you wish later to view a different segment, simply reload the trace file and specify the new segment number when prompted. Reloading is done via the "View" or "Express" items in the "Trace" menu.
Communication Timeline WindowAcross the top of the timeline window is a control and information area. The trace data is displayed below this on timelines, one per process in the traced application. The state of the application at a particular time is represented by the corresponding traffic light color. Green represents running, red represents blocked waiting on communication and yellow represents time spent inside an MPI function not blocked on communication (we call this system overhead time as it typically represents time doing data conversion, message packing, etc).
The dial can be used to select a time point at which the process states are to be displayed. In the overview window the process states at the dial time are displayed in hexagon form. As with snapshot mode more detailed information on a process can be obtained by bringing up its focus window. The dial may be moved by clicking with the left button in the trace view area or via the VCR controls. Below the VCR controls are displayed from left to right, the time of the left edge of the displayed timeline, the current dial time and the time of the right edge of the displayed timeline.
To the right of the VCR controls is displayed the current magnification. When a trace file is loaded XMPI chooses an initial scaling factor and sets this to be the 1x1 magnification. You can increase and decrease the magnification using the zoom and un-zoom buttons.
A segment of the currently displayed timeline can be selected by dragging the right mouse button in the timeline display area. Upon release of the right button the display is zoomed to show the selected segment. To cancel a drag in progress, drag the cursor up or down out of the timeline display area.
How Communication Is Represented
- A collective communication is represented for each process by contiguous line segments showing the time spent in system overhead and the time spent blocked waiting for communication. No lines are drawn connecting the processes participating in the collective communication.
- For both the send and receive process contiguous line segments are drawn showing the time spent in system overhead and the time spent blocked waiting for the communication to complete. A line is drawn connecting the send to the receive. It originates at the beginning of the send segments and is drawn to the end of the matching receive segments.
- At the time a non-blocking send or receive is initiated a system overhead segment is drawn. When the communication is completed via a wait or test, segments showing system overhead and blocking time are drawn. Lines are drawn between matching sends and receives, except in this case the line is drawn from the segment where the send was initiated to where the corresponding receive completed.
- If a non-blocking communication is completed inside a wait/test function XMPI will show the function name in the focus window as the wait/test function followed in parentheses by the send/receive function being completed. For example, if an MPI_Issend() is completed inside an MPI_Wait(), the function will read MPI_Wait (MPI_Issend).
- Owing to the use of trace segments or the dropping of overflow traces (see lamtrace(1)) there may be send or receive traces which have no match in the trace data. In these cases a short stub line is drawn out from a send or in to a receive.
Kiviat WindowWhen viewing a trace file, the "Kiviat" button or "Kiviat" item from the "Trace" menu brings up the Kiviat window. This window displays, in a segmented pie-chart format, the cumulative time up to the current dial time, spent by each process in the running, overhead and blocked states.
MESSAGE SOURCE MATRIXThe message source window displays a square matrix of process message queue lengths. For each process it shows the number of queued messages from each other process in the application. It can be brought up while monitoring a running application or while viewing a trace file, by selecting the "Matrix" button or "Matrix" item in the "Trace" menu.
DATATYPE WINDOWThe datatype window displays a textual representation of the type map of an MPI datatype. This window is associated at any instant with a particular process and mode. The associated process is shown in the window's banner and the mode is indicated by a traffic light or message queue icon shown in the left part of the window. When in process mode the datatype being shown, if any, is the datatype argument of the MPI function the process is executing. When in message mode the datatype is that of the current message aggregate selected in the process focus window. Switching between processes and modes is effected via the datatype buttons in the process focus windows.
The type map might not fit completely into the default size window. Simply resize the window to see the whole map.
SWITCHING INFORMATION SOURCESXMPI will gather and display information from either the currently executing application or a trace file. When an application is launched from XMPI, the information source is the executing application and the "Snap" button is active. Though the application may be producing trace data, the "Snap" button does not use it, but instead acquires information from debugging hooks in the MPI implementation. At any moment, an existing trace file may be loaded into XMPI or the currently accumulating trace data may be fetched from the MPI implementation, stored in a file, and loaded. This action changes the information source to the loaded trace file. Information display is now controlled from the dial in the timeline window and not from the "Snap" button, which is now inactive. Though the application may still be running, the timeline dial does not use the runtime debugging hooks, but instead acquires information from the loaded trace file. Upon the closing of the trace window XMPI will return to snapshot mode if there is a running application.
RESOURCESXMPI defines the following application resources.
- command that is run to provide help. The default is typically a command which fires up a Web browser to view a help page. You should change this to invoke your favourite browser.
- process rank font in hexagon
- total message count font in hexagon (may need to be adjusted to fit inside message icon)
- color used to highlight the processes in an intracommunicator or in the the local group of an intercommunicator
- color used to highlight the processes in the remote group of an intercommunicator
- color used for the zoom selection rubber band
- if True use a dashed line rubber band to show the zoom selection otherwise use a solid line
- width of the zoom selection rubber band
XMPI gets important default resources from the application defaults file, XMPI. If this file is not installed in the X11 default directory, its directory can be added to the XAPPLRESDIR environment variable.
LIMITATIONSAn application must be started by XMPI to be monitored by it.
When using the fast client-to-client communication mode process states in snapshot mode are always shown as running and no useful information is shown in the process focus windows.
XMPI uses lamclean(1). Errors reported by this tool will still print to standard output. A shorter message will appear in an XMPI error dialog.