[Intel-gfx] [PATCH V2 6/6] drm/i915:Use the coarse ping-pong mechanism based on drm fd to dispatch the BSD command on BDW GT3

[Daniel Vetter]

On Mon, Apr 14, 2014 at 12:21:44PM +0800, Zhao Yakui wrote:
> V1->V2: Follow Daniel's comment and use the simple ping-pong mechanism.
> This is only to add the support of dual BSD rings on BDW GT3 machine.
> The further optimization will be considered in another patch set.
> 
> The BDW GT3 has two independent BSD rings, which can be used to process the
> video commands. To be simpler, it is transparent to user-space driver/middle.
> Instead the kernel driver will decide which ring is to dispatch the BSD video
> command.
> 
> As every BSD ring is powerful, it is enough to dispatch the BSD video command
> based on the drm fd. In such case it can play back video stream while encoding
> another video stream. The coarse ping-pong mechanism is used to determine
> which BSD ring is used to dispatch the BSD video command.
> 
> Signed-off-by: Zhao Yakui <yakui.zhao at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_dma.c            |    3 +++
>  drivers/gpu/drm/i915/i915_drv.h            |    3 +++
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c |   37 +++++++++++++++++++++++++++-
>  3 files changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 0b38f88..4d27cf4 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1572,6 +1572,7 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
>  	spin_lock_init(&dev_priv->backlight_lock);
>  	spin_lock_init(&dev_priv->uncore.lock);
>  	spin_lock_init(&dev_priv->mm.object_stat_lock);
> +	atomic_set(&dev_priv->bsd_cmd_counter, 0);
>  	mutex_init(&dev_priv->dpio_lock);
>  	mutex_init(&dev_priv->modeset_restore_lock);
>  
> @@ -1929,6 +1930,8 @@ void i915_driver_postclose(struct drm_device *dev, struct drm_file *file)
>  {
>  	struct drm_i915_file_private *file_priv = file->driver_priv;
>  
> +	if (file_priv && file_priv->bsd_ring)
> +		file_priv->bsd_ring = NULL;
>  	kfree(file_priv);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index ac5598c3..68e8166 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1466,6 +1466,8 @@ struct drm_i915_private {
>  	struct i915_dri1_state dri1;
>  	/* Old ums support infrastructure, same warning applies. */
>  	struct i915_ums_state ums;
> +	/* the lock for dispatch video commands on two BSD rings */
> +	atomic_t bsd_cmd_counter;

You're still using atomic_t for no real good reason.
gen8_dispatch_bsd_ring is always called with the dev->struct_mutex lock
held, so there's really no reason for it.
-Daniel

>  };
>  
>  static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
> @@ -1673,6 +1675,7 @@ struct drm_i915_file_private {
>  
>  	struct i915_hw_context *private_default_ctx;
>  	atomic_t rps_wait_boost;
> +	struct  intel_ring_buffer *bsd_ring;
>  };
>  
>  /*
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index 341ec68..720ef17 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -999,6 +999,34 @@ i915_reset_gen7_sol_offsets(struct drm_device *dev,
>  	return 0;
>  }
>  
> +/**
> + * Find one BSD ring to dispatch the corresponding BSD command.
> + * The Ring ID is returned.
> + */
> +static int gen8_dispatch_bsd_ring(struct drm_device *dev,
> +				  struct drm_file *file)
> +{
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct drm_i915_file_private *file_priv = file->driver_priv;
> +
> +	/* Check whether the file_priv is using one ring */
> +	if (file_priv->bsd_ring)
> +		return file_priv->bsd_ring->id;
> +	else {
> +		/* If no, use the ping-pong mechanism to select one ring */
> +		int counter, ring_id;
> +		smp_mb__before_atomic_inc();
> +		counter = atomic_inc_return(&dev_priv->bsd_cmd_counter);
> +		if (counter % 2 == 0)
> +			ring_id = VCS;
> +		else
> +			ring_id = VCS2;
> +
> +		file_priv->bsd_ring = &dev_priv->ring[ring_id];
> +		return ring_id;
> +	}
> +}
> +
>  static int
>  i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>  		       struct drm_file *file,
> @@ -1043,7 +1071,14 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>  
>  	if ((args->flags & I915_EXEC_RING_MASK) == I915_EXEC_DEFAULT)
>  		ring = &dev_priv->ring[RCS];
> -	else
> +	else if ((args->flags & I915_EXEC_RING_MASK) == I915_EXEC_BSD) {
> +		if (HAS_BSD2(dev)) {
> +			int ring_id;
> +			ring_id = gen8_dispatch_bsd_ring(dev, file);
> +			ring = &dev_priv->ring[ring_id];
> +		} else
> +			ring = &dev_priv->ring[VCS];
> +	} else
>  		ring = &dev_priv->ring[(args->flags & I915_EXEC_RING_MASK) - 1];
>  
>  	if (!intel_ring_initialized(ring)) {
> -- 
> 1.7.10.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch