The goal of the Statistical Preview is to help users select a frame for viewing. It consists of two windows. The major window shown in Figure , is titled ``View & Frame Selector'', but is usually called ``Preview''. It contains a graphical representation of all the activities going on during the run of the program sppm. Activities in ``Preview'' are computed in the following way. The whole duration of the job sppm is divided into 512 time bins. For each time bin, there are counters for each state and arrow that occur in the time bin. The counter of each state/arrow will be incremented by a statistical weight that equals the ratio of the duration of state/arrow to the width of time bin that the state/arrow is in. Because of this definition of the statistical weight for each state/arrow, very short duration states or arrows become statistically insignificant and will not contribute much to the accumulative activities of all the states and arrows. The visual consequence is that states/arrows with very short duration are not noticeable in ``Preview''. The graphical representation of the activities of the logfiles is, by default, in accumulative histogram mode, which can be turned on/off through the button selection sequence Graph->Type->Bar. The other mode is the noncumulative curve mode which can be enabled by the button selection sequence Graph->Type->Line. It is shown in Figure . Since it is noncumulative, as in histogram mode, it distinguishes the relative importance of various states.
``Preview'' and its corresponding ``Legend'' windows meant to be used side by side to help you select frames that are of interest. If some of the states displayed in the ``Preview'' seem useless or confusing, it can be easily removed. First highlight the state through click on the name in the ``Legend''; then click on Select/Deselect button to remove them from ``Preview''. In Figure , all MPI and system-related states are deselected in ``Preview'' to highlight the user-defined states ``layout'', ``setup'', ``bdrys'' and ``glbl''. It becomes apparent that all the communications between the user MPI processes are done in regular interval. Also, all communications(i.e. arrows) are within the user-defined state ``bdrys''. Assume you are interested in the behavior of the program between the last two instances of MPI_Allreduce. Then you can simply click on None to deselect all the states and arrows, highlight MPI_Allreduce, then click Select/Deselect to display only MPI_Allreduce in the ``Preview''. Now click on any region between the last two MPI_Allreduce's in the ``Preview''. Then the frame index is changed from 0 to 2, and a red line is positioned in the middle of the frame 2 and is also between the last two instances of MPI_Allreduce. Now select the properties of the frame to be viewed. Most end users who are interested in the performance of the code sppm should select the Connected States option with either MPI-Process or Thread view. If you are interested in how the operating system dispatches threads among CPUs allocated for the job, you may want to select the Disconnected States option in the Processor view.