[PATCH v7 2/5] drm/panfrost: Add fdinfo support GPU load metrics
AngeloGioacchino Del Regno
angelogioacchino.delregno at collabora.com
Thu Sep 28 11:24:55 UTC 2023
Il 27/09/23 23:29, Adrián Larumbe ha scritto:
> The drm-stats fdinfo tags made available to user space are drm-engine,
> drm-cycles, drm-max-freq and drm-curfreq, one per job slot.
>
> This deviates from standard practice in other DRM drivers, where a single
> set of key:value pairs is provided for the whole render engine. However,
> Panfrost has separate queues for fragment and vertex/tiler jobs, so a
> decision was made to calculate bus cycles and workload times separately.
>
> Maximum operating frequency is calculated at devfreq initialisation time.
> Current frequency is made available to user space because nvtop uses it
> when performing engine usage calculations.
>
> It is important to bear in mind that both GPU cycle and kernel time numbers
> provided are at best rough estimations, and always reported in excess from
> the actual figure because of two reasons:
> - Excess time because of the delay between the end of a job processing,
> the subsequent job IRQ and the actual time of the sample.
> - Time spent in the engine queue waiting for the GPU to pick up the next
> job.
>
> To avoid race conditions during enablement/disabling, a reference counting
> mechanism was introduced, and a job flag that tells us whether a given job
> increased the refcount. This is necessary, because user space can toggle
> cycle counting through a debugfs file, and a given job might have been in
> flight by the time cycle counting was disabled.
>
> The main goal of the debugfs cycle counter knob is letting tools like nvtop
> or IGT's gputop switch it at any time, to avoid power waste in case no
> engine usage measuring is necessary.
>
> Add also documentation file explaining the possible values for fdinfo's
Also add a documentation file explaining .....
or
Moreover, add a documentation file explaining .....
> engine keystrings and Panfrost-specific drm-curfreq-<keystr> pairs.
>
> Signed-off-by: Adrián Larumbe <adrian.larumbe at collabora.com>
> Reviewed-by: Boris Brezillon <boris.brezillon at collabora.com>
> Reviewed-by: Steven Price <steven.price at arm.com>
Nitpick apart:
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com>
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