Re: [PATCH] drm/i915: Convert the forcewake worker into a timer func

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Feb 28, 2014 at 09:02:38AM +0000, Chris Wilson wrote:
> We don't want to suffer scheduling delay when turning off the GPU after
> waking it up to touch registers. Ideally, we only want to keep the GPU
> awake for the register access sequence, with a single forcewake dance on
> the first access and release immediately after the last. We set a timer
> on the first access so that we only dance once and on the next scheduler
> tick, we drop the forcewake again.
> 
> This moves the cleanup routine from the common i915 workqueue to a timer
> func so that we don't anger powertop, and drop the forcewake again
> quicker.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |    2 +-
>  drivers/gpu/drm/i915/intel_uncore.c |   15 ++++++---------
>  2 files changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index eb31c45..9416b03 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -508,7 +508,7 @@ struct intel_uncore {
>  	unsigned fw_rendercount;
>  	unsigned fw_mediacount;
>  
> -	struct delayed_work force_wake_work;
> +	struct timer_list force_wake_timer;
>  };
>  
>  #define DEV_INFO_FOR_EACH_FLAG(func, sep) \
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index c628414..140a9f0 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -289,10 +289,8 @@ void vlv_force_wake_put(struct drm_i915_private *dev_priv,
>  	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
>  }
>  
> -static void gen6_force_wake_work(struct work_struct *work)
> +static void gen6_force_wake_timer(struct drm_i915_private *dev_priv)
>  {
> -	struct drm_i915_private *dev_priv =
> -		container_of(work, typeof(*dev_priv), uncore.force_wake_work.work);
>  	unsigned long irqflags;
>  
>  	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
> @@ -405,9 +403,8 @@ void gen6_gt_force_wake_put(struct drm_i915_private *dev_priv, int fw_engine)
>  	spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
>  	if (--dev_priv->uncore.forcewake_count == 0) {
>  		dev_priv->uncore.forcewake_count++;
> -		mod_delayed_work(dev_priv->wq,
> -				 &dev_priv->uncore.force_wake_work,
> -				 1);
> +		mod_timer_pinned(&dev_priv->uncore.force_wake_timer,
> +				 jiffies + 1);
>  	}
>  	spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);

Should we use the timer to delay the forcewake release from register
read/write functions too? Or maybe do it only for register
read/write since gen6_gt_force_wake_get/put are rather rare and I
wouldn't expect significant forcewake ping-pong after the put.

>  
> @@ -681,8 +678,8 @@ void intel_uncore_init(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> -	INIT_DELAYED_WORK(&dev_priv->uncore.force_wake_work,
> -			  gen6_force_wake_work);
> +	setup_timer(&dev_priv->uncore.force_wake_timer,
> +		    gen6_force_wake_timer, (unsigned long)dev_priv);
>  
>  	if (IS_VALLEYVIEW(dev)) {
>  		dev_priv->uncore.funcs.force_wake_get = __vlv_force_wake_get;
> @@ -794,7 +791,7 @@ void intel_uncore_fini(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> -	flush_delayed_work(&dev_priv->uncore.force_wake_work);
> +	del_timer_sync(&dev_priv->uncore.force_wake_timer);
>  
>  	/* Paranoia: make sure we have disabled everything before we exit. */
>  	intel_uncore_sanitize(dev);
> -- 
> 1.7.9.5
> 
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-- 
Ville Syrjälä
Intel OTC