[PATCH] drm/i915: Improve debug Kconfig texts a bit

[PATCH] drm/i915: Improve debug Kconfig texts a bit

[Daniel Vetter]

We're not consistently recommending these for developers only.

I stumbled over this due to DRM_I915_LOW_LEVEL_TRACEPOINTS, which was
added in

commit 354d036fcf70654cff2e2cbdda54a835d219b9d2
Author: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Date:   Tue Feb 21 11:01:42 2017 +0000

    drm/i915/tracepoints: Add request submit and execute tracepoints

to "alleviate the performance impact concerns."

Which is nonsense.

Tvrtko and Joonas pointed out on irc that the real (but undocumented
reason) was stable abi concerns for tracepoints, see

https://lwn.net/Articles/705270/

and the specific change that was blocked around tracepoints:

https://lwn.net/Articles/442113/

Anyway to make it a notch clearer why we have this Kconfig option
consistly add the "Recommended for driver developers only." to it and
all the other debug options we have.

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/i915/Kconfig.debug | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
index 2ca88072d30f..f27c0b5873f7 100644
--- a/drivers/gpu/drm/i915/Kconfig.debug
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -215,6 +215,8 @@ config DRM_I915_LOW_LEVEL_TRACEPOINTS
 	  This provides the ability to precisely monitor engine utilisation
 	  and also analyze the request dependency resolving timeline.
 
+	  Recommended for driver developers only.
+
 	  If in doubt, say "N".
 
 config DRM_I915_DEBUG_VBLANK_EVADE
@@ -228,6 +230,8 @@ config DRM_I915_DEBUG_VBLANK_EVADE
 	  is exceeded, even if there isn't an actual risk of missing
 	  the vblank.
 
+	  Recommended for driver developers only.
+
 	  If in doubt, say "N".
 
 config DRM_I915_DEBUG_RUNTIME_PM
@@ -240,4 +244,6 @@ config DRM_I915_DEBUG_RUNTIME_PM
 	  runtime PM functionality. This may introduce overhead during
 	  driver loading, suspend and resume operations.
 
+	  Recommended for driver developers only.
+
 	  If in doubt, say "N"
-- 
2.32.0.rc2

Re: [PATCH] drm/i915: Improve debug Kconfig texts a bit

[Joonas Lahtinen]

Quoting Daniel Vetter (2021-07-02 23:17:08)
> We're not consistently recommending these for developers only.
> 
> I stumbled over this due to DRM_I915_LOW_LEVEL_TRACEPOINTS, which was
> added in
> 
> commit 354d036fcf70654cff2e2cbdda54a835d219b9d2
> Author: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Date:   Tue Feb 21 11:01:42 2017 +0000
> 
>     drm/i915/tracepoints: Add request submit and execute tracepoints
> 
> to "alleviate the performance impact concerns."
> 
> Which is nonsense.

I think that was the original reason why the patch was developed and
it got merged primarily for the latter reason. Unfortunately the patch
commit messages don't always get rewritten.

> Tvrtko and Joonas pointed out on irc that the real (but undocumented
> reason) was stable abi concerns for tracepoints, see
> 
> https://lwn.net/Articles/705270/
> 
> and the specific change that was blocked around tracepoints:
> 
> https://lwn.net/Articles/442113/
> 
> Anyway to make it a notch clearer why we have this Kconfig option
> consistly add the "Recommended for driver developers only." to it and
> all the other debug options we have.
> 
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas

> ---
>  drivers/gpu/drm/i915/Kconfig.debug | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> index 2ca88072d30f..f27c0b5873f7 100644
> --- a/drivers/gpu/drm/i915/Kconfig.debug
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -215,6 +215,8 @@ config DRM_I915_LOW_LEVEL_TRACEPOINTS
>           This provides the ability to precisely monitor engine utilisation
>           and also analyze the request dependency resolving timeline.
>  
> +         Recommended for driver developers only.
> +
>           If in doubt, say "N".
>  
>  config DRM_I915_DEBUG_VBLANK_EVADE
> @@ -228,6 +230,8 @@ config DRM_I915_DEBUG_VBLANK_EVADE
>           is exceeded, even if there isn't an actual risk of missing
>           the vblank.
>  
> +         Recommended for driver developers only.
> +
>           If in doubt, say "N".
>  
>  config DRM_I915_DEBUG_RUNTIME_PM
> @@ -240,4 +244,6 @@ config DRM_I915_DEBUG_RUNTIME_PM
>           runtime PM functionality. This may introduce overhead during
>           driver loading, suspend and resume operations.
>  
> +         Recommended for driver developers only.
> +
>           If in doubt, say "N"
> -- 
> 2.32.0.rc2
> 

Re: [PATCH] drm/i915: Improve debug Kconfig texts a bit

[Daniel Vetter]

On Mon, Jul 05, 2021 at 02:48:23PM +0300, Joonas Lahtinen wrote:
> Quoting Daniel Vetter (2021-07-02 23:17:08)
> > We're not consistently recommending these for developers only.
> > 
> > I stumbled over this due to DRM_I915_LOW_LEVEL_TRACEPOINTS, which was
> > added in
> > 
> > commit 354d036fcf70654cff2e2cbdda54a835d219b9d2
> > Author: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Date:   Tue Feb 21 11:01:42 2017 +0000
> > 
> >     drm/i915/tracepoints: Add request submit and execute tracepoints
> > 
> > to "alleviate the performance impact concerns."
> > 
> > Which is nonsense.
> 
> I think that was the original reason why the patch was developed and
> it got merged primarily for the latter reason. Unfortunately the patch
> commit messages don't always get rewritten.
> 
> > Tvrtko and Joonas pointed out on irc that the real (but undocumented
> > reason) was stable abi concerns for tracepoints, see
> > 
> > https://lwn.net/Articles/705270/
> > 
> > and the specific change that was blocked around tracepoints:
> > 
> > https://lwn.net/Articles/442113/
> > 
> > Anyway to make it a notch clearer why we have this Kconfig option
> > consistly add the "Recommended for driver developers only." to it and
> > all the other debug options we have.
> > 
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Matthew Brost <matthew.brost@intel.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> 
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Pushed to drm-intel-gt-next, thanks for taking a look.
-Daniel

> 
> Regards, Joonas
> 
> > ---
> >  drivers/gpu/drm/i915/Kconfig.debug | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> > index 2ca88072d30f..f27c0b5873f7 100644
> > --- a/drivers/gpu/drm/i915/Kconfig.debug
> > +++ b/drivers/gpu/drm/i915/Kconfig.debug
> > @@ -215,6 +215,8 @@ config DRM_I915_LOW_LEVEL_TRACEPOINTS
> >           This provides the ability to precisely monitor engine utilisation
> >           and also analyze the request dependency resolving timeline.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N".
> >  
> >  config DRM_I915_DEBUG_VBLANK_EVADE
> > @@ -228,6 +230,8 @@ config DRM_I915_DEBUG_VBLANK_EVADE
> >           is exceeded, even if there isn't an actual risk of missing
> >           the vblank.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N".
> >  
> >  config DRM_I915_DEBUG_RUNTIME_PM
> > @@ -240,4 +244,6 @@ config DRM_I915_DEBUG_RUNTIME_PM
> >           runtime PM functionality. This may introduce overhead during
> >           driver loading, suspend and resume operations.
> >  
> > +         Recommended for driver developers only.
> > +
> >           If in doubt, say "N"
> > -- 
> > 2.32.0.rc2
> > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch