ECM-Model

Knowledge base how to setup the ECM model inputs

Dependencies

• LIKWID
• LaTeX and TikZ for plotting (Step 3)

Current limitations

• Only for streaming kernels
• No hardware counter measurements included for verification

Workflow

Step 1: Running benchmarks

The script ./bench_scan_size.sh has to be used to run the benchmark and collect the performance results. The script takes in a run configuration file which defines the likwid-bench benchmarks to be runs, the result folders and hardware settings. Some sample configuration files can be found in the run_config folder. The benchmark runs streaming kernels with different stream/array size. For example to run with the settings in run_config/casclakesp2_config.txt file the following can be used:

/bench_scan_size.sh run_config/casclakesp2_config.txt

NB: If some basic performance relevant hardware configuration is not set as described in the config file, the script will pre-exit with a message "Hardware not configured properly".

Step 2: ECM Generator

This step is optional. The step generates the ECM model plots corresponding to the benchmarks run in the previous step. The ECM generation requires two basic inputs: application model and machine model.

2.1 Application model

The application model defines the properties of the benchmark. The application model is defined using a file written into the folder ecm_generator/application_model which indicates the number and type of streams seen in the benchmark.

• Read-only specifies the number of steams/arrays that have to be just read
• Write-only specifies the number of steams/arrays that have to be just written
• Read-Write specifies the number of steams/arrays that have to be both read and written

Examples of the application model files can be found in the ecm_generator/application_model folder.

2.2 Machine model

The machine model determines the machine capabilities. It is defined using files written to ecm_generator/machine_model folder. The files carry information like:

• CL_size specifies the cacheline size in bytes
• [cache-name]_read_bw specifies the read bandwidth between the given [cache-name] cache level and its higher hierarchy. For example L1_read_bw indicates read bandwidth between L1 and registers
• [cache-name]_write_bw specifies the write bandwidth between the given [cache-name] cache level and its higher hierarchy. For example L1_write_bw indicates write bandwidth between L1 and registers
• [cache-name]_shared_bw specifies the bandwidth between the given [cache-name] cache level and its higher hierarchy when a different resource becomes a bottleneck. For example L1_shared_bw indicates the bandwidth when the common (for both reads and writes) address generation unit (AGU) becomes a bottleneck.
• [cache-name]_WA indicates whether write-allocate is applicable for the cache
• [cache-name]_VICTIM indicates whether the cache is a victim cache
• [cache-name]_SIZE indicates the cache size in kB
• ECM_hypothesis indicates the overlap hypothesis of the given hardware under a given setting.

2.3 Generating ECM data

The script ecm_generator/ecm.sh generates the ECM model prediction data. It takes the application model and machine model defined above as input. For example to generate ECM model with application model ecm_generator/application_model/copy.config and machine model ecm_generator/machine_model/casclakesp2_nps1.config following command can be used:

cd ecm_generator
./ecm.sh "application_model/copy.config" "machine_model/casclakesp2_nps1.config" 

Note that in general only the application model (2.1) and machine model (2.2) has to be defined. The generation of ECM model (2.3) need not be done manually as indicated here and will be done automatically when calling the plotting script. See next section.

Step 3: Plotting results

The script ./generate_all_plots.sh runs ecm script ecm_generator/ecm.sh (2.3) and collects the performance measurements collected in Step 1 to generate final plots. The script requires the location of folder where performance measurements are collected (as specified through configuration file in Step 1) and the machine file corresponding to the machine model. For example to plot the results collected in results/casclakesp2/nps2/avx512/ with the ECM model corresponding to machine file ecm_generator/machine_model/casclakesp2/nps2/avx512/casclakesp2_nps2_avx512.config, the following command should be used:

./generate_all_plots.sh results/casclakesp2/nps2/avx512/ ecm_generator/machine_model/casclakesp2/nps2/avx512/casclakesp2_nps2_avx512.config

The plots are then generated in a folder called plots located in the same directory given in the input (results/casclakesp2/nps2/avx512/ in above example). Plots (in pdf format) for different benchmarks as well as an overall compiled plot called ecm.pdf could be found in the plots directory.