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| Computer Sciences |
| General Overview |
| Home > Computer Sciences > Performance Tools > Paraver > General Overview |  |
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Paraver: the flexible analysis tool
Paraver is a flexible performance visualization and analysis tool that can be used to analyze
Expressive power, flexibility and the capability of efficiently handling large traces are key features addressed in the design of Paraver. The clear and modular structure of Paraver plays a significant role towards achieving these targets. Some Paraver features are the support for
The following are major features of the Paraver philosophy and functionality Views Paraver offers a minimal set of views on a trace. The philosophy behind the design was that different types of views should only be supported if they provide qualitatively different types of information. Frequently, visualization tools tend to offer many different views of the parallel program behavior. Nevertheless, it is often the case that only a few of them are actually used by developers. The other views are too complex, too specific or not adapted to the developer needs. Paraver differentiates three types of views:
The
single type of graphic view is flexible enough to represent visually a
large amount of information and to be the reference for the
quantitative analysis. The Paraver view consists of a time diagram with
one line for each represented object. The types of objects displayed by
Paraver are closely related to the parallel programming model concepts
and to the execution resources. In the first group, the objects
considered are: workload, application, task and thread. Although most
frequently is used to visualize a single application, Paraver can
display the concurrent execution of several paralel applications. In
the resources group, the objects considerd are: system, node and CPU. Paraver
displayed information consists of three elements: a time dependent value (called
semantic value) for each represented object, flags that correspond to punctual
events within a represented object, and communication lines that relate the
displayed objects. The visualization module determines how each of these
elements is displayed. With it is possible to change the types of representation,
colors and scales. The visualization
module blindly represents the values and events passed to it, without assigning
to them any pre-conceived semantics. This plays a key role in the flexibility
of the tool. The semantics of the displayed information (activity of a thread,
cache misses, sequence of functions called ) lies in the mind of the user.
Paraver specifies a trace format but no actual semantics for the encoded values.
What it offers is a set of building blocks (filter and semantic modules) to
transform the trace in the visualization process. Depending on how you generate the trace
and combine the building blocks, you can get a huge number of different semantic
magnitudes visualized. Expressive
power
The separation between the visualization power (how to display) and the semantic module (value to display) offers a flexibility and expressive power above what is frequently encountered in other tools. Many visualization tools include a filtering module to reduce the amount of displayed information. In Paraver, the filtering module is in front of the semantic one. The result is added flexibility in the generation of the value returned by the semantic module. Paraver
semantic module is structured as a hierarchy of functions that are composed
to compute the value passed to the visualization module. Each level of function
corresponds to one level in the hierarchical structure of the process/resource
model on which Paraver relies.
For example, when displaying threads,
a thread function computes the semantic value from the records that describe
the thread activity. When displaying tasks, the thread function is applied
to all the threads of the task and a task function is used to reduce those
values to the one that represents the task. When displaying processors,
a processor function is applied to all the threads assigned to that processor. Combining very simple semantic functions (Sum, Sign, State As Is, Last Event Value ....), at each level, a tremendous expressive power results. Besides the typical processor time diagram, for example it is possible to display:
Qualitative behavior display is not sufficient to draw conclusions on where the problems are or how to improve the code. Detailed numbers are needed to sustain what otherwise are subjective impressions. The quantitative analysis functions are applied after the semantic module in the same way as the visualization module. Again here, very simple functions (average, count....) at this level combined with the power of the semantic module result in a large variety of supported measures. The quantitative analysis module of Paraver can be applied to any user selected section of the visualized application and has two variants: The 1D analysis computes the values on the semantic function of the selected window. It includes features such as being able to measure times, count events or compute average value of the displayed magnitude. Some examples are: The
2D analysis
allows to merge the semantic function of two windows or to analyze the
communications for each source-target pair. It includes features such
as being able to measure times, averages, number of bytes.... Some examples are: After some experience, maximizing the amount of information obtainable by the combination of semantical analysis functions becomes a challenging issue for Paraver users. Multiple traces In order to support comparative analyses, the simultaneous visualization of several traces is needed. Paraver can concurrently display multiple traces, making it possible to use the same scales and synchronized animation in several windows. This multi-trace feature supports detailed comparisons that otherwise would become very subjective or cumbersome. For example, it is possible to compare:
Large traces A requirement for Paraver was that the whole operation of the tool has to be very fast in order to make it usable and capable to maintain the developer interest. Handling traces in the range of tenths to hundreds of MB is an important objective of Paraver to enable the analysis of real programs. Easy window dimensioning, forward and backward animation and zooming are supported. Several windows with different scales can be displayed simultaneously. Even on very large traces, the quantitative analysis can be carried out with great precision because the starting and end point of the analysis can be selected on different windows. The tracefiles are usually managed in ASCII format to allow portability between different platforms, but the tool domapfile can be used to translate the tracefile to binary format reducing its size and the time needed to load it. Cooperative analysis The configuration files allow to share the knowledge and expertise using Paraver. Once a desired view is obtained, it can be stored in a configuration file to apply it again to the same tracefile or to a different one. Sharing the tracefiles and the corresponding configuration files allow to easily share views of the trace and the information obtained. As the configuration file describes the options set on the filter, semantic and visualizer modules it is independent on the tracefile and once defined could be used for different runs and different applications. Derived Metrics Following the philosophy of Paraver, the derived metrics are simple and powerful: the user can combine two displaying windows of a tracefile using very simple operators (add, product, maximum,..) to obtain a new semantic function. Applying this procedure recursively, it is possible to obtain semantic functions like:
Batch processing
In some cases it can be interesting to use all the analysis capabilities of Paraver without using the GUI interface. This is the case of:
To allow these type of studies, we have developed Paramedir (in Spanish means "to meassure"). Paramedir is a new version of Paraver that does not have GUI. The basic commands (trough the binary or API interfaces) allow to load a tracefile, load a configuration file and save the results of the analysis in a text file. The strengh of this version is that it uses the same configuration files than Paraver so the same analysis carried out with the gui can be saved on a configuration file and later applied to many tracefiles with Paramedir. We do not recommend to use Paramedir blindly to do performance analysis. Our experience is that it is very important to keep looking at the timelines details that some average values can mask.
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