PMaC Prediction Framework
The PMaC Prediction Framework is an implementation of an automated prediction model. A prediction model is a calculable expression that takes as parameters attributes of application software, input data, and target machine hardware (and possibly other factors) and computes, as output, expected performance. The expected performance in this case is the expected runtime of the application.
The PMaC Framework operates by using the following three elements.
- Machine Profile
- Characterization of the rates at which a machine can (or is projected to) carry out fundamental operations abstract from any particular application.
- Application Signature
- Detailed summaries of the fundamental operations carried out by the application independent of any particular machine.
- Convolution Methods
- Algebraic mappings of the Application Signatures on to the Machine profiles to arrive at a performance prediction.
Figure 1. An outline of the performance prediction model
The following sections outline the prediction process in more detail.
Obtaining a Machine Profile
For the purposes of the PMaC prediction framework a Machine Profile is a characterizations of the rates at which a machine can (or is projected to) carry out fundamental operations, abstract from any particular application.
Memory and network performance are measured by simple benchmarks run on 1 to 2 nodes of a target system to create the machine profile.
- Memory Operations
- The performance of a machines memory sub-system is measured using PMaC's MultiMAPS Benchmark. MultiMAPS measures the bandwidth achieved by the machine while retrieving a variety of data sizes using different strides and line sizes. MultiMAPS is only run on a single node of the system. Figure 2 shows a sample of the data given by MultiMAPS for 3 different systems.
- Network Operations
- Network performance is measured by a simple mpi ping-pong benchmark run on 2 nodes of the system in various ways.
Figure 2: Sample data collected from MultiMaps
Obtaining an Application Signature
Two categories of operations are observed in order to obtain an application signature, memory and network operations, collected by PMaCinst/PEBIL and MPIDTrace respectivly.
- PMaCinst is a binary re-writer for the PowerPC platform that instruments memory and floating-point operations. The memory address stream of those operations is processed on-the-fly through cache simulator. The cache simulator is capable of simulating >20 different cache structures. Output is a summary for each cache structure
- PEBIL is a binary instrumentation toolkit for x86/Linux platforms, and performs the same functions as PMaCinst within the prediction framework.
- PSiNS Tracer
- An instrumentation tool (link time) to capture information about MPI calls including the time spentin each call, argument values to the call, and hardware counter information about the execution. PSiNS Tracer combines the minimal features of MPIDTrace and IPM tools.
- Network operations (mpi calls) are recorded by a tool called MPIDTrace. MPIDTrace is part of the Dimemas project, developed by the European Center for Parallelism at Barcelona. MPIDTrace creates an event trace file, which is used by Dimemas for simulation in one of the convolution steps.
There are two convolution steps. The first step, the PMaC Convolver, models the work done on the processor in between communication events. This model work or time is used by Dimemas to simulate the execution of the application on the target system.
- PMaC Convolver
- This convolution step uses the trace results from PMaCinst and the memory profile data to produce an estimated time for the work done on the processor in between communication events on the target machine for that application.
- PSiNS Simulator
- Similar to Dimemas, PSiNS Simulator uses the estimated time from the PMaC convolver along with MPI call trace produced by different tools (PSiNS Tracer, MPIDTrace) to simulate the execution of the application on the target system and emits the execution time as well as significant information on the decompostion of execution time to program components similar to the information given by IPM.
- Dimemas uses the estimated time from the PMaC convolver along with the event trace produced by MPIDtrace to simulate the execution of the application on the target system.