LIKWID is developed by FAU for Performance Optimization, Modeling, and Architecture Analysis * Bringing the thinking back to the performance engineer. * Open-source * Command-line and Software Lib interface. No GUI * x86 Architecture (Intel & AMD) with initial support for Nvidia GPUs

LIKIWID Toolset is available in SCC as a module, thus before using LIKWID a user need to load their preferred LIKWID version module to set the environment correctly.

(base) gwdu101:25 17:17:18 ~ > module show likwid
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  /opt/sw/modules/21.12/cascadelake/Core/likwid/5.2.0.lua:
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
...

(base) gwdu101:25 17:17:24 ~ > 
(base) gwdu101:25 17:18:33 ~ > module load likwid
(base) gwdu101:25 17:18:43 ~ >

The following tasks can be performed by LIKWID:

$ likwid-topology
$ likwid-powermeter

Examples of node-architecture for SCC's amp016:

$ likwid-pin
$ likwid-mpirun

$ likwid-features
$ likwid-setFrequencies

* Using the available hardware counters to measure events that characterises the interaction between software and hardware * Uses a light-weight marker API for code instrumentation

$ likwid-perfctr

• Quantify sustainable performance limits
• Separate influences considering isolated instruction code snippets
• Reverse-egineer processor features
• Discover hardware bugs

$ likwid-bench
$ likwid-memsweeper

• Thread topology: How processor IDs map on physical compute resources
• Cache topology: How processors share the cache hierarchy
• Cache properties: Detailed information about all cache levels
• NUMA topology: NUMA domains and memory sizes
• GPU topology: GPU information

• Explicitly supports pthread and the OpenMP implementations of Intel and GNU gcc
• Only used with “pthread_create” API call which are dynamically linked with the static placement of threads.

• a lightweight command-line application to configure and read out hardware performance data
• Can be used as a wrapper (no modification in the application) or by adding “Marker_API” functions inside the code
• There are preconfigured performance groups with useful event sets and derived metrics
• Since *likwid-perfctr* measures all events on the specified CPUs, it is necessary for processes and threads to dedicated resources.
• This can be done by pinning the application manually or using the built-in functionality

• An outstanding feature of LIKWID
• Organizes and combines micro-architecture events and counters with e.g. run-time and clock speed
• Provides a set of derived metrics for efficient analysis
• They are read on the fly without compilation by command-line selection
• Are found in the path “${INSTALL_PREFIX}/share/likwid”

Examples of using “likwid-perfctr” on SCC's amp016 node

• Use option “-a” to see available performance groups:

• Use “likwid-perfctr -g CLOCK” to measure the clock speed.

• Use “likwid-perfctr -g FLOPS_DP” to measure the Arithmetic Intensity in double precision.

• Use “likwid-perfctr -g MEM” to measure the bandwidth of primary memory.

• Enables measurements of user-defined code regions.
• The Marker API offers 6 functions (for C/C++) to measure named regions
• Activated by “-DLIKWID_PERFORM” to compiler calls

    LIKWID_MARKER_INIT //global initialization
    LIKWID_MARKER_THREADINIT //individual thread initialization
    LIKWID_MARKER_START('compute') //Start a code region named 'compute'
    LIKWID_MARKER_STOP('compute') //Stop the code region named 'compute'
    LIWKID_MARKER_SWITCH //Switches perfromance group or event set in a round-robin fashion
    LIKWID_MARKER_CLOSE //global finalization
    

• [LIKWID](https://github.com/RRZE-HPC/likwid/wiki)