===== VTune =====

VTune is a performance profiler from Intel and is available on the HPC cluster.

General information of Intel : https://software.intel.com/en-us/get-started-with-vtune-linux-os

The VTUne commands have prefix amplxe- *. The most important are: 

  * amplxe-cl  #< launches VTune Command Line.
  * amplxe-gui #< launches VTune with a graphical interface.

Profiling steps:

  * Data collection (collect) 
  * Analysis of the results
 
   
==== Collect ====

To collect profiling data, run the executable via amplxe-cl,
specifying an action between the following: https://software.intel.com/en-us/vtune-amplifier-help-amplxe-cl-actions 

The action necessary to collect data about performance is **collect**.
This action requires an option to specify the type of analysis, including: 
   * **hotspots**: Identify your most time-consuming source code.
   * **concurrency**: Analyze how your application is using available logical CPU cores, discover where parallelism is incurring synchronization overhead, and identify potential candidates for parallelization.
   * **hpc-performance**: Identify opportunities to optimize CPU, memory, and FPU utilization for compute-intensive or throughput applications.
   * **memory-access**: Measure a set of metrics to identify memory access related issues (for example, specific for NUMA architectures).

Command example: 
  amplxe-cl -collect hotspots -result-dir <dirname>  home/test/myApplication

=== Result analysis ===

The off-line analysis of the collected data can be done in a graphical way with amplxe-gui:

   amplxe-gui <dirname>





==== HPC (UNIPR) ====

Connect to gui.hpc.unipr.it and perform an interactive job; eg: 
   srun -N1 -n68 -p knl --account=<account name>
   
   > module load intel # (include vtune too)
   > amplxe-cl -collect hotspots -result-dir <dirname>  home/test/myApplication
   > exit
  
It is preferable to launch on the University HPC cluster amplxe-gui from gui.hpc.unipr.it: 
    
  module load intel 
  amplxe-gui  <dirname>
  
  
=== MARCONI (CINECA)  ===

On Marconi you can 'submit an interactive session, in which to perform both the collect and the data analysis (amplxe-gui does not work on the login machine), such as:
  srun -N1 -n68 -t 00:30:00  -A <account name> -p knl --pty bash
  
  > module load intel vtune
  > amplxe-cl  -collect hpc-performance -result-dir myresults bin/myexe <options>
  > amplxe-gui  myresults
  > exit


=== Debug Info ===

To include debugging information in the results (for example the source code) you need to fill in with the option

<code>
   -gdwarf-2 
</code>