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

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Date:   Tue, 25 Jul 2023 10:38:07 +0200
From:   Maxime Ripard <mripard@...nel.org>
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 Thu, Apr 27, 2023 at 03:14:39PM +0200, Maxime Ripard wrote:
> 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?

I'd still like to address this. We spend ~90% of the DRM kunit tests
execution time executing those two tests, which doesn't seem like a
reasonable thing to do.

I'm fine with doing that work, but I'd still need to figure out what
those tests are doing exactly. Can someone help?

Maxime

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