Intel tuning tools
Intel provide a set of tuning tools that can be quite useful. The following sections will give an overview of the tools and provide a quick guide of the scope of the different tools and for which type of tuning and what kind of programming model that are applicable for, vectorization, threading, MPI.
Below is a list of tools that can be used to analyses the application, starting from text analysis of the source code to massive parallel MPI runs.
- Intel compiler, analysis of source code.
- Intel XE-Advisor, analysis of Vectorization.
- Intel XE-Inspector, analysis of threads and memory.
- Intel VTune-Amplifier, analysis and profiling of complete program performance.
- Intel MPI, profile the MPI calls.
- Intel Trace Analyzer, analysis of MPI communication.
The PRACE Best Practice Guide for the Intel processor Knights Landing: [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#tuning.section] contain a nice review of the Intel tools and how to use them. Chapter 7 is about tuning. Only chapters 1 and 2 are specific to the Knights Landing processor.
A short overview is given here with links to the relevant tools. The Best Practice Guide provide an overview of the tools with a focus on sampling. The actual usage of the different tools is only covered in depth by the Intel documentation. Even with the documentation it can be hard to start using the tools in an effective way. Attending Intel training is advised.
Intel compiler - optimization report
Compiler flags provide a mean of controlling the optimization done by the compiler. There are a rich set of compiler flags and directives that will guide the compiler's optimization process. The details of all these switches and flags can be found in the documentation, in this guide we'll provide a set of flags that normally gives acceptable performance. It must be said that the defaults are set to request a quite high level of optimization, and the default might not always be the optimal set. Not all the aggressive optimizations are numerically accurate, computer evaluation of an expression is as we all know quite different from paper and pencil evaluation.
Please consult the BPG guide section about the Intel Compiler at: [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#id-126.96.36.199]
To use the Intel compiler one of the Intel compiler modules must be loaded, an example is :
module load intel/2018b
Intel MPI library
The MPI Perf Snapshot is a built in lightweight tool that will provide some helpful information with little effort from the user. Link your program with -profile=vt and simply issue the -mps flag to the mpirun command (some environment need to be set up first, but this is quite simple).
mpiifort -o ./photo_tr.x -profile=vt *.o mpirun -mps -np 16 ./photo_tr.x
More information at the Best Practice Guide : [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#id-188.8.131.52]
Vectorization Advisor is an analysis tool that lets you identify if loops utilize modern SIMD instructions or not, what prevents vectorization, what is performance efficiency and how to increase it. Vectorization Advisor shows compiler optimization reports in user-friendly way, and extends them with multiple other metrics, like loop trip counts, CPU time, memory access patterns and recommendations for optimization.
More information at the Best Practice Guide : [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#XE-Advisor]
To have access to the XE-Advisor load the designated module, an example is:
module load Advisor/2018_update3
Then launch the advisor in GUI or text version.
Using the GUI X11 version over long distances might be somewhat slow.
Intel Inspector is a dynamic memory and threading error checking tool for users developing serial and multithreaded applications. The tuning tool XE-advisor as tool tailored for threaded shared memory applications (it can also collect performance data for hybrid MPI jobs using a command line interface). It provide analysis of memory and threading that might prove useful for tuning of any application.
More information at the Best Practice Guide : [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#id-184.108.40.206]
To use the XE-Inspector us the Inspector module, like :
module load Inspector/2018_update3
To launch the GUI:
Intel VTune Amplifier
Intel VTune Amplifier provides a rich set of performance insight into CPU performance, threading performance and scaleability, bandwidth, caching and much more. Originally a tool for processor development, hence the strong focus on hardware counters.
Analysis is fast and easy because VTune Amplifier understands common threading models and presents information at a higher level that is easier to interpret. Use its powerful analysis to sort, filter and visualize results on the timeline and on your source. However, the sheer amount of information is sometimes overwhelming and in some cases intimidating. To really start using VTune Amplifier some basic training is suggested.
More information at the Best Practice Guide : [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#id-220.127.116.11]
To get access to the Vtune Amplifier load the corresponding module, like:
ml load VTune/2018_update3
For a run-through example see a VTune case study.
Intel Trace Analyzer
Intel Trace Analyzer and Collector is a graphical tool for understanding MPI application behavior, quickly finding bottlenecks, improving correctness, and achieving high performance for parallel cluster applications based on Intel architecture. Improve weak and strong scaling for small and large applications with Intel Trace Analyzer and Collector. The collector tool is closely linked to the MPI library and the profiler library must be compiled and linked with the application. There is an option to run using a preloaded library, but the optimal way is to link in the collector libraries at build time.
More information at the Best Practice Guide : [http://www.prace-ri.eu/best-practice-guide-knights-landing-january-2017/#id-18.104.22.168]
To use Intel Trace Analyzer load the corresponding module, e.g.
ml load itac/2019.4.036