Re: [PATCH net-next v6 2/3] selftests: tc-testing: add fq_pie per-flow class stats test

["Hemendra M. Naik" <hemendranaik@gmail.com>]

Thank you for the review. Replies are inline below.

> Can this case ever pass with a released iproute2? [...] Turning that
> blob into the literal tokens "prob", "delay" and "deficit" requires the
> companion iproute2 change [...] which is not merged. [...] Would it make
> sense to add a 'dependsOn' probe so the case skips when the userspace
> support is absent, or to assert only what current tc prints?
>
> A related question: the pattern hard-codes the exact label text and
> ordering of the not-yet-reviewed userspace formatter. If the iproute2
> side lands with different wording or field order [...] does this
> kernel selftest then break while the kernel itself is unchanged?

We'd like to keep the check as it is, without a dependsOn probe.
There are several cases that were written against, and still assume, 
newer tc wording with no dependsOn guard at all, e.g.:
  - tc-tests/qdiscs/fq.json (commit 3007d8712c9b, "adjust fq test to
    latest iproute2")
  - tc-tests/infra/qdiscs.json (commit 56acc7f51974, "Adapt test's
    output to HFSC's iproute2 printing changes")
  - tc-tests/actions/police.json (commit b7df2e7eaef7, "Adapt tc
    police action tests for Gb rounding changes")
  - tc-tests/actions/bpf.json (commit ac2944abe4d7, "Be compatible
    with newer tc output")

We're doing the same thing here: this test is paired with the
companion iproute2 patch, same as those cases were paired with the tc
versions they were written for.

> Can this case fail intermittently depending on the host environment?
> The assertion needs a backlogged flow at the instant the dump runs
> [...] its exit status is discarded with '|| true'. If ping is not
> installed, or the installed iputils rejects the fractional -i 0.001 /
> -W 0.01 arguments, the fq_pie queue stays empty [...] Would it be
> better to check the ping result, or to enqueue traffic in a way that
> does not depend on neighbour solicitation timing?

We'd like to keep the ping command as it is. The same pattern
('-W 0.01 -i 0.001 ... || true') is already used, unguarded, elsewhere
in this test suite - for example in case a4c3 in
tools/testing/selftests/tc-testing/tc-tests/infra/qdiscs.json. So this
isn't a new risk, it's existing practice..