Re: [PATCH 3/3] media: hantro: add per-context fdinfo usage stats

[Detlev Casanova]

Hi Nicolas,

On 6/12/26 11:18, Nicolas Dufresne wrote:
> Hi,
>
> Le vendredi 12 juin 2026 à 10:26 -0400, Detlev Casanova a écrit :
> > From: Christopher Healy <healych@xxxxxxxxxx>
> >
> > Add per-file-descriptor hardware utilization tracking to the Hantro
> > VPU stateless codec driver, exposed via /proc/<pid>/fdinfo/<fd>.
> >
> > Record a ktime timestamp when each job is submitted to hardware in
> > device_run(), and accumulate the elapsed nanoseconds when the job
> > completes in hantro_job_finish(). Report the accumulated time along
> > with the current clock frequency through the new V4L2 show_fdinfo
> > callback.
> >
> > The output uses a media- key prefix with the following keys:
> >    media-driver:           driver name
> >    media-engine-<eng>:     accumulated busy time in nanoseconds
> >    media-maxfreq-<eng>:    maximum engine frequency in Hz
> >    media-curfreq-<eng>:    current engine frequency in Hz
> >
> > Where <eng> is "decoder" or "encoder" depending on the context.
> >
> > This enables userspace monitoring tools to compute per-process decoder
> > and encoder utilization. The current and max frequency keys report the
> > same value today since the driver lacks devfreq support, but will
> > diverge once DVFS is added, allowing userspace to approximate true
> > capacity utilization without any fdinfo code changes. A future series
> > can add hardware cycle counter support (via media-cycles-<eng>) for
> > exact utilization under DVFS, with no changes to the existing uAPI.
> >
> > Signed-off-by: Christopher Healy <healych@xxxxxxxxxx>
> > Signed-off-by: Detlev Casanova <detlev.casanova@xxxxxxxxxxxxx>
> > ---
> >   drivers/media/platform/verisilicon/hantro.h     |  5 +++++
> >   drivers/media/platform/verisilicon/hantro_drv.c | 22 ++++++++++++++++++++++
> >   2 files changed, 27 insertions(+)
> >
> > diff --git a/drivers/media/platform/verisilicon/hantro.h b/drivers/media/platform/verisilicon/hantro.h
> > index 0353de154a1e..10287e5cebac 100644
> > --- a/drivers/media/platform/verisilicon/hantro.h
> > +++ b/drivers/media/platform/verisilicon/hantro.h
> > @@ -16,6 +16,7 @@
> >   #include <linux/videodev2.h>
> >   #include <linux/wait.h>
> >   #include <linux/clk.h>
> > +#include <linux/ktime.h>
> >   #include <linux/reset.h>
> >   
> >   #include <media/v4l2-ctrls.h>
> > @@ -268,6 +269,10 @@ struct hantro_ctx {
> >   	struct hantro_postproc_ctx postproc;
> >   	bool need_postproc;
> >   
> > +	/* Statistics for debugging and performance measurements. */
> > +	ktime_t start_time;
> > +	u64 total_ns;
> > +
> >   	/* Specific for particular codec modes. */
> >   	union {
> >   		struct hantro_h264_dec_hw_ctx h264_dec;
> > diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
> > index 2e81877f640f..139c2e6a83aa 100644
> > --- a/drivers/media/platform/verisilicon/hantro_drv.c
> > +++ b/drivers/media/platform/verisilicon/hantro_drv.c
> > @@ -90,6 +90,8 @@ static void hantro_job_finish(struct hantro_dev *vpu,
> >   			      struct hantro_ctx *ctx,
> >   			      enum vb2_buffer_state result)
> >   {
> > +	ctx->total_ns += ktime_to_ns(ktime_sub(ktime_get(), ctx->start_time));
> > +
> >   	pm_runtime_put_autosuspend(vpu->dev);
> >   
> >   	clk_bulk_disable(vpu->variant->num_clocks, vpu->clocks);
> > @@ -186,6 +188,8 @@ static void device_run(void *priv)
> >   
> >   	v4l2_m2m_buf_copy_metadata(src, dst);
> >   
> > +	ctx->start_time = ktime_get();
> > +
> >   	if (ctx->codec_ops->run(ctx))
> >   		goto err_cancel_job;
> >   
> > @@ -701,10 +705,28 @@ static int hantro_release(struct file *filp)
> >   	return 0;
> >   }
> >   
> > +static void hantro_show_fdinfo(struct seq_file *m, struct file *f)
> > +{
> > +	struct hantro_ctx *ctx = file_to_ctx(f);
> > +	struct hantro_dev *vpu = ctx->dev;
> > +
> > +	seq_printf(m, "media-driver:\t%s\n", DRIVER_NAME);
> > +	seq_printf(m, "media-engine-%s:\t%llu ns\n",
> > +		   ctx->is_encoder ? "encoder" : "decoder",
> > +		   ctx->total_ns);
> > +	seq_printf(m, "media-maxfreq-%s:\t%lu Hz\n",
> > +		   ctx->is_encoder ? "encoder" : "decoder",
> > +		   clk_get_rate(vpu->clocks[0].clk));
> > +	seq_printf(m, "media-curfreq-%s:\t%lu Hz\n",
> > +		   ctx->is_encoder ? "encoder" : "decoder",
> > +		   clk_get_rate(vpu->clocks[0].clk));
> Similar to what was done in DRM helpers, I would create a common structure,
> maybe in a v4l2-stats library (or some better name). The driver would fill that
> structure directly, or through helpers (such as software timer helper, cycle
> count translation helper), and finally, this show_fd_info() would be a one
> liners, just like DRM do.
>
> This will ensure full consistency in the trace, and avoid possible future
> unresolvable compatibility issue due to past mistakes. If we ever let a bug
> through (of course we won't :-D) all driver will have the same bug, and it will
> be easier to not break userspace.
Yes, that makes a lot of sense actually, And will also help with the 
ftrace HW info if we have stats and debug info centralized in v4l2
> Nicolas
>
> > +}
> > +
> >   static const struct v4l2_file_operations hantro_fops = {
> >   	.owner = THIS_MODULE,
> >   	.open = hantro_open,
> >   	.release = hantro_release,
> > +	.show_fdinfo = hantro_show_fdinfo,
> >   	.poll = v4l2_m2m_fop_poll,
> >   	.unlocked_ioctl = video_ioctl2,
> >   	.mmap = v4l2_m2m_fop_mmap,