Slow Loop (literally):

dd if=/dev/zero of=./test bs=10M count=1
losetup /dev/loop1 ./test
mkdir /sys/fs/cgroup/test
echo '7:1 rbps=1048576' > /sys/fs/cgroup/test/io.max
echo $$ > /sys/fs/cgroup/test/cgroup.procs
pv /dev/loop1 > /dev/null

https://andrestc.com/post/cgroups-io/