linux-kernel - Re: [PATCH v5 9/9] drm: selftest: convert drm

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Date:   Thu, 27 Apr 2023 15:14:39 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Maíra Canal <maira.canal@....br>,
        David Gow <davidgow@...gle.com>,
        Daniel Latypov <dlatypov@...gle.com>, brendanhiggins@...gle.com
Cc:     Isabella Basso <isabbasso@...eup.net>, magalilemes00@...il.com,
        tales.aparecida@...il.com, mwen@...lia.com, andrealmeid@...eup.net,
        siqueirajordao@...eup.net, Trevor Woerner <twoerner@...il.com>,
        leandro.ribeiro@...labora.com, n@...aprado.net,
        Daniel Vetter <daniel@...ll.ch>,
        Shuah Khan <skhan@...uxfoundation.org>,
        David Airlie <airlied@...ux.ie>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        michal.winiarski@...el.com,
        Javier Martinez Canillas <javierm@...hat.com>,
        José Expósito <jose.exposito89@...il.com>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Arthur Grillo <arthur.grillo@....br>
Subject: Re: [PATCH v5 9/9] drm: selftest: convert drm_mm selftest to KUnit

Hi,

On Fri, Jul 08, 2022 at 05:30:52PM -0300, Maíra Canal wrote:
> From: Arthur Grillo <arthur.grillo@....br>
> 
> Considering the current adoption of the KUnit framework, convert the
> DRM mm selftest to the KUnit API.
> 
> Signed-off-by: Arthur Grillo <arthur.grillo@....br>
> Tested-by: David Gow <davidgow@...gle.com>
> Acked-by: Daniel Latypov <dlatypov@...gle.com>
> Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>
> Signed-off-by: Maíra Canal <maira.canal@....br>

I'm very late to the party, but I'd like to discuss that patch some more.

Two tests (drm_test_mm_reserve, drm_test_mm_insert) in it take a super
long time to run (about 30s each on my machine).

If we run all the DRM tests and VC4 tests, each of those two are longer
to run than all the ~300 tests combined. About 100 times longer.

I don't think that running for so long is reasonable, and for multiple
reasons:

  - While I don't know drm_mm well, it doesn't look like any of those
    tests do something that really should take this long. I'm especially
    skeptical about the fact that we test each operation 8192 times by
    default.

  - It makes using kunit more tedious than it should be. Like I said, on
    a very capable machine, running the all the DRM and VC4 tests takes
    about 50s with those two tests, ~0.4s without.

  - The corollary is that it will get in the way of people that really
    want to use kunit will just remove those tests before doing so,
    defeating the original intent.


I understand that it came from selftests initially, but I think we
should rewrite the tests entirely to have smaller, faster tests. It's
not clear to me why those tests are as complicated as they are though.

Also, going forward we should probably put disencourage tests running
that long. Could Kunit timeout/warn after a while if a test is taking
more than X seconds to run?

Maxime

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