freq-bench

freq-bench copied to clipboard

This is the supporting benchmark for the blog post Gathering Intel on Intel AVX-512 Transitions.

This benchmark relies heavily on the perf_events subsystem and so only runs on Linux.

Build

This project provides a makefile and building should be as simple as:

make

Checking perf_event_paranoid

To run these tests you need a /proc/sys/kernel/perf_event_paranoid setting of 1 or less, or to be running as root. Many modern system are setting this to 3, a very conservative setting. If the value on your system is greater than 1, you can either set it (until reboot) to 1 like so:

echo 1 | sudo tee /proc/sys/kernel/perf_event_paranoid

Or you can run the tests as root (e.g., `sudo ./bench)

Running

The benchmark includes several tests. You can run them all like this (this will crash pretty quickly on platforms without AVX-512):

./bench

You can run a specific test by providing its name:

./bench vporymm

You can list the available tests:

./bench list tests

Generating Results

You can run all the test required for generating the data used in the post using the ./data.sh scripts. First you should set your TSC (time stamp counter as read by rstsc) frequency as the MHZ variable in the environment. The benchmark application itself has detection of the TSC frequency, you can check the value on your system by running:

./bench dummy |& grep 'tsc freq'

Set that value as MHZ in your environment, like so:

export MHZ=3200

Next, choose a prefix for your result files to identify them, this defaults to test if you don't set any:

export PREFIX=blah
# this second prefix is used specificaly for the voltage related tests
export PREFIXV=blah

Then you can collect most of the data like this:

scripts/data.sh

This generates the results in the ./results dir by default. This generates all the results except for those related to voltage. To generate those, you need to jump through a few hoops, because voltage readings require MSR access. First, you must have msr-tools installed, however that works on your platform (e.g., apt install msr-tools on Ubuntu). Then you can either run data.sh as root, like so:

sudo MHZ=$MHZ DO_VOLTS=1 scripts/data.sh

The DO_VOLTS=1 indicates to the script that it should run only the voltage tests. This causes the files written to ./results to be owned by root (unless the files already existed with different ownership), so you should chown them to your current user after. You can also run this as a non-root user but you have to jump though some hoops (this is probably not entirely safe, certainly not on any host with untrusted users or code):

# set the special msr files world readable
sudo chmod a+r /dev/cpu/*/msr
# give the bench binary the caps needed to read the msr files (not needed on all systems)
sudo setcap cap_sys_rawio=ep ./bench
# run the test as non-root
DO_VOLTS=1 scripts/data.sh

Generating Plots

Once the results are generated, you can generate the plots with:

scripts/plots.sh

That will show the plots, one by one, in matplotlib's interactive viewer. To write them out to SVG files, just provide the OUTDIR environment variable:

mkdir plots
OUTDIR=./plots scripts/plots.sh

The script expects all the result files to exist, feel free to comment out some lines if you've just generated partial results. You can also pass the script a regex and it will only generate plots whose title matches the regex. For example, the following generates only the 3 voltage plots:

./scripts/plots.sh Voltage