Re: [PATCH] drm/i915: Make vblank evade warnings optional

[Daniel Vetter <daniel@ffwll.ch>]

On Sun, May 07, 2017 at 08:12:52PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Add a new Kconfig option to enable/disable the extra warnings
> from the vblank evade code. For now we'll keep the warning
> about an actually missed vblank always enabled as that can have
> an actual user visible impact. But if we miss the deadline
> othrwise there's no real need to bother the user with that.
> We'll want these warnings enabled during development however
> so that we can catch regressions.
> 
> Based on the reports it looks like this is still very easy
> to hit on SKL, so we have more work ahead of us to optimize
> the crtiical section further.
> 
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Reported-by: Jens Axboe <axboe@kernel.dk>
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Fixes: e1edbd44e23b ("drm/i915: Complain if we take too long under vblank evasion.")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/Kconfig.debug  | 13 +++++++++++++
>  drivers/gpu/drm/i915/intel_sprite.c |  7 +++++--
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
> index e091809a9a9e..49db32fa6524 100644
> --- a/drivers/gpu/drm/i915/Kconfig.debug
> +++ b/drivers/gpu/drm/i915/Kconfig.debug
> @@ -87,3 +87,16 @@ config DRM_I915_LOW_LEVEL_TRACEPOINTS
>            and also analyze the request dependency resolving timeline.
>  
>            If in doubt, say "N".
> +
> +config DRM_I915_DEBUG_VBLANK_EVADE
> +	bool "Enable extra debug warnings for vblank evasion"
> +	depends on DRM_I915
> +	default n
> +	help
> +	  Choose this option to turn on extra debug warnings for the
> +	  vblank evade mechanism. This gives a warning every time the
> +	  the deadline allotted for the vblank evade critical section
> +	  is exceeded, even if there isn't an actual risk of missing
> +	  the vblank.
> +
> +	  If in doubt, say "N".
> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
> index f7d431427115..8c87c717c7cd 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/intel_sprite.c
> @@ -198,12 +198,15 @@ void intel_pipe_update_end(struct intel_crtc *crtc, struct intel_flip_work *work
>  			  ktime_us_delta(end_vbl_time, crtc->debug.start_vbl_time),
>  			  crtc->debug.min_vbl, crtc->debug.max_vbl,
>  			  crtc->debug.scanline_start, scanline_end);
> -	} else if (ktime_us_delta(end_vbl_time, crtc->debug.start_vbl_time) >
> -		   VBLANK_EVASION_TIME_US)
> +	}
> +#ifdef CONFIG_DRM_I915_DEBUG_VBLANK_EVADE
> +	else if (ktime_us_delta(end_vbl_time, crtc->debug.start_vbl_time) >
> +		 VBLANK_EVASION_TIME_US)
>  		DRM_WARN("Atomic update on pipe (%c) took %lld us, max time under evasion is %u us\n",
>  			 pipe_name(pipe),
>  			 ktime_us_delta(end_vbl_time, crtc->debug.start_vbl_time),
>  			 VBLANK_EVASION_TIME_US);
> +#endif
>  }
>  
>  static void
> -- 
> 2.10.2
> 

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