linux-kernel - Re: [PATCH v2] drm/vc4: Add a debugfs entry to disable/enable the load tracker

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Message-ID: <87r2f2patf.fsf@anholt.net>
Date:   Fri, 30 Nov 2018 12:30:52 -0800
From:   Eric Anholt <eric@...olt.net>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v2] drm/vc4: Add a debugfs entry to disable/enable the load tracker

Paul Kocialkowski <paul.kocialkowski@...tlin.com> writes:

> In order to test whether the load tracker is working as expected, we
> need the ability to compare the commit result with the underrun
> indication. With the load tracker always enabled, commits that are
> expected to trigger an underrun are always rejected, so userspace
> cannot get the actual underrun indication from the hardware.
>
> Add a debugfs entry to disable/enable the load tracker, so that a DRM
> commit expected to trigger an underrun can go through with the load
> tracker disabled. The underrun indication is then available to
> userspace and can be checked against the commit result with the load
> tracker enabled.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>

Given that the load tracker is going to be conservative and say things
will underrun even when they might not in practice, will this actually
be useful for automated testing?  Or is the intent to make it easier to
tune the load tracker by disabling it so that you can experiment freely?

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