[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

[Zhao Yakui]

On Mon, 2014-04-14 at 01:22 -0600, Daniel Vetter wrote:
> 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.

If the struct_mutex is used in the gen8_dispatch_bsd_ring, I can remove
the atomic_t. 
It seems that the struct_mutex is a big lock and it is used very
frequently(i915_gem.c, i915_dma.c and so on). In my point it is a little
heavier than the atomic_t if one counter is increased and returned. 

If you think that the mutex is better than atomic, I will follow your
advice.

Thanks.
    Yakui

> -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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