[PATCH 0/2][V2] io.latency test for blktests

[Josef Bacik <josef@toxicpanda.com>]

v1->v2:
- dropped my python library, TIL about jq.
- fixed the spelling mistakes in the test.

-- Original message --

This patchset is to add a test to verify io.latency is working properly, and to
add all the supporting code to run that test.

First is the cgroup2 infrastructure which is fairly straightforward.  Just
verifies we have cgroup2, and gives us the helpers to check and make sure we
have the right controllers in place for the test.

The second patch brings over some python scripts I put in xfstests for parsing
the fio json output.  I looked at the existing fio performance stuff in
blktests, but we only capture bw stuff, which is wonky with this particular test
because once the fast group is finished the slow group is allowed to go as fast
as it wants.  So I needed this to pull out actual jobtime spent.  This will give
us flexibility to pull out other fio performance data in the future.

The final patch is the test itself.  It simply runs a job by itself to get a
baseline view of the disk performance.  Then it creates 2 cgroups, one fast and
one slow, and runs the same job simultaneously in both groups.  The result
should be that the fast group takes just slightly longer time than the baseline
(I use a 15% threshold to be safe), and that the slow one takes considerably
longer.  Thanks,

Josef