linux-kernel - Re: [PATCH v3 1/1] drm/panfrost: Replace fdinfo's profiling debugfs knob with sysfs

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Date: Tue, 12 Mar 2024 00:47:06 +0000
From: Adrián Larumbe <adrian.larumbe@...labora.com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Tvrtko Ursulin <tursulin@...ulin.net>, robh@...nel.org, 
	steven.price@....com, airlied@...il.com, daniel@...ll.ch, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, corbet@....net, 
	kernel@...labora.com, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 1/1] drm/panfrost: Replace fdinfo's profiling debugfs
 knob with sysfs

On 11.03.2024 11:02, Boris Brezillon wrote:
> On Wed, 6 Mar 2024 08:33:47 +0000
> Tvrtko Ursulin <tursulin@...ulin.net> wrote:
> 
> > On 06/03/2024 01:56, Adrián Larumbe wrote:
> > > Debugfs isn't always available in production builds that try to squeeze
> > > every single byte out of the kernel image, but we still need a way to
> > > toggle the timestamp and cycle counter registers so that jobs can be
> > > profiled for fdinfo's drm engine and cycle calculations.
> > > 
> > > Drop the debugfs knob and replace it with a sysfs file that accomplishes
> > > the same functionality, and document its ABI in a separate file.
> > > 
> > > Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> > > ---
> > >   .../testing/sysfs-driver-panfrost-profiling   | 10 +++++
> > >   Documentation/gpu/panfrost.rst                |  9 ++++
> > >   drivers/gpu/drm/panfrost/Makefile             |  2 -
> > >   drivers/gpu/drm/panfrost/panfrost_debugfs.c   | 21 ----------
> > >   drivers/gpu/drm/panfrost/panfrost_debugfs.h   | 14 -------
> > >   drivers/gpu/drm/panfrost/panfrost_device.h    |  2 +-
> > >   drivers/gpu/drm/panfrost/panfrost_drv.c       | 41 ++++++++++++++++---
> > >   drivers/gpu/drm/panfrost/panfrost_job.c       |  2 +-
> > >   8 files changed, 57 insertions(+), 44 deletions(-)
> > >   create mode 100644 Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> > >   delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.c
> > >   delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.h
> > > 
> > > diff --git a/Documentation/ABI/testing/sysfs-driver-panfrost-profiling b/Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> > > new file mode 100644
> > > index 000000000000..1d8bb0978920
> > > --- /dev/null
> > > +++ b/Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> > > @@ -0,0 +1,10 @@
> > > +What:		/sys/bus/platform/drivers/panfrost/.../profiling
> > > +Date:		February 2024
> > > +KernelVersion:	6.8.0
> > > +Contact:	Adrian Larumbe <adrian.larumbe@...labora.com>
> > > +Description:
> > > +		Get/set drm fdinfo's engine and cycles profiling status.
> > > +		Valid values are:
> > > +		0: Don't enable fdinfo job profiling sources.
> > > +		1: Enable fdinfo job profiling sources, this enables both the GPU's
> > > +		   timestamp and cycle counter registers.
> > > \ No newline at end of file
> > > diff --git a/Documentation/gpu/panfrost.rst b/Documentation/gpu/panfrost.rst
> > > index b80e41f4b2c5..51ba375fd80d 100644
> > > --- a/Documentation/gpu/panfrost.rst
> > > +++ b/Documentation/gpu/panfrost.rst
> > > @@ -38,3 +38,12 @@ the currently possible format options:
> > >   
> > >   Possible `drm-engine-` key names are: `fragment`, and  `vertex-tiler`.
> > >   `drm-curfreq-` values convey the current operating frequency for that engine.
> > > +
> > > +Users must bear in mind that engine and cycle sampling are disabled by default,
> > > +because of power saving concerns. `fdinfo` users and benchmark applications which
> > > +query the fdinfo file must make sure to toggle the job profiling status of the
> > > +driver by writing into the appropriate sysfs node::
> > > +
> > > +    echo <N> > /sys/bus/platform/drivers/panfrost/[a-f0-9]*.gpu/profiling  
> > 
> > A late thought - how it would work to not output the inactive fdinfo 
> > keys when this knob is not enabled?
> > 
> > Generic userspace like gputop already handles that and wouldn't show the 
> > stat. Which may be more user friendly than showing stats permanently at 
> > zero. It may be moot once you add the auto-toggle to gputop (or so) but 
> > perhaps worth considering.
> 
> I agree with Tvrtko, if the line being printed in fdinfo relies on some
> sysfs knob to be valid, we'd rather not print the information in that
> case, instead of printing zero.

Me too. I'll go first change both gputop and nvtop to make sure they use the new
sysfs knob for Panfrost, and then submit a new patch that handles printing of
the drm-cycles-* and drm-engine-* stats depending on the profiling knob state.