Re: [PATCH v3 1/8] media: hantro: Trace hevc hw cycles performance register

From: Ezequiel Garcia <ezequiel@collabora.com>
To: Benjamin Gaignard <benjamin.gaignard@collabora.com>,
	hverkuil@xs4all.nl, p.zabel@pengutronix.de, mchehab@kernel.org,
	shawnguo@kernel.org, s.hauer@pengutronix.de, festevam@gmail.com,
	gregkh@linuxfoundation.org, mripard@kernel.org,
	paul.kocialkowski@bootlin.com, wens@csie.org,
	jernej.skrabec@siol.net, emil.l.velikov@gmail.com,
	andrzej.p@collabora.com, jc@kynesim.co.uk,
	jernej.skrabec@gmail.com, nicolas@ndufresne.ca
Cc: kernel@pengutronix.de, linux-imx@nxp.com,
	linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/8] media: hantro: Trace hevc hw cycles performance register
Date: Fri, 18 Jun 2021 15:58:46 -0300	[thread overview]
Message-ID: <418311dac48d3a29b4fe9e363f7d4e82c360f586.camel@collabora.com> (raw)
In-Reply-To: <20210618131526.566762-2-benjamin.gaignard@collabora.com>

Hi Benjamin,

On Fri, 2021-06-18 at 15:15 +0200, Benjamin Gaignard wrote:
> After each hevc decoded frame trace the hardware performance.
> It provides the number of hw cycles spend per decoded macroblock.
> 

Please add some documentation about how these are supposed
to be used. It will be easier to discuss after seeing
things in actiion.

A good place for the documentation would be:

https://www.kernel.org/doc/html/latest/admin-guide/media/v4l-drivers.html

[..]
> @@ -22,6 +23,21 @@ static inline void hantro_write_addr(struct hantro_dev *vpu,
>         vdpu_write(vpu, addr & 0xffffffff, offset);
>  }
>  
> +void hantro_g2_hevc_dec_done(struct hantro_ctx *ctx)

I'm worried about the runtime cost this would have.

I see other drivers (i915, panfrost) seem to have an ioctl
to enable the perf counters.

Perhaps we don't need an ioctl, but a module param would be enough
for now.

> +{
> +       const struct hantro_hevc_dec_ctrls *ctrls = &ctx->hevc_dec.ctrls;
> +       const struct v4l2_ctrl_hevc_sps *sps = ctrls->sps;
> +       struct hantro_dev *vpu = ctx->dev;
> +       u32 hw_cycles = 0;
> +       u32 mbs = (sps->pic_width_in_luma_samples *
> +                  sps->pic_height_in_luma_samples) >> 8;
> +
> +       if (mbs)
> +               hw_cycles = vdpu_read(vpu, G2_HW_PERFORMANCE) / mbs;
> +
> +       trace_hantro_hevc_perf(ctx, hw_cycles);
> +}
> +
> 
[..]
> +
> +TRACE_EVENT(hantro_hevc_perf,
> +       TP_PROTO(struct hantro_ctx *ctx, u32 hw_cycles),
> +
> +       TP_ARGS(ctx, hw_cycles),
> +
> +       TP_STRUCT__entry(
> +               __field(int, minor)
> +               __field(u32, hw_cycles)
> +       ),
> +
> +       TP_fast_assign(
> +               __entry->minor = ctx->fh.vdev->minor;

Tracking performance per minor doesn't seem useful,
we'd like to track per-fd (i.e. per context).

Thanks,
Ezequiel