[Intel-gfx] [PATCH 27/38] drm/i915: Reduce locking inside swfinish ioctl

[Daniel Vetter]

On Fri, Jun 03, 2016 at 05:55:42PM +0100, Chris Wilson wrote:
> We only need to take the struct_mutex if the object is pinned to the
> display engine and so requires checking for clflush. (The race with
> userspace pinning the object to a framebuffer is irrelevant.)
> 
> v2: Use access once for compiler hints (or not as it is a bitfield)
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index a4f949038d50..b78f9df1894c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1265,25 +1265,28 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>  {
>  	struct drm_i915_gem_sw_finish *args = data;
>  	struct drm_i915_gem_object *obj;
> -	int ret = 0;
> -
> -	ret = i915_mutex_lock_interruptible(dev);
> -	if (ret)
> -		return ret;
> +	int ret;
>  
>  	obj = i915_gem_object_lookup(file, args->handle);
> -	if (!obj) {
> -		ret = -ENOENT;
> -		goto unlock;
> -	}
> +	if (!obj)
> +		return -ENOENT;
>  
>  	/* Pinned buffers may be scanout, so flush the cache */
> -	if (obj->pin_display)
> +	if (obj->pin_display) {

READ_ONCE(obj->pin_display)?

> +		ret = i915_mutex_lock_interruptible(dev);
> +		if (ret)
> +			goto unref;
> +
>  		i915_gem_object_flush_cpu_write_domain(obj);
>  
> -	i915_gem_object_put(obj);
> -unlock:
> -	mutex_unlock(&dev->struct_mutex);
> +		i915_gem_object_put(obj);
> +		mutex_unlock(&dev->struct_mutex);
> +	} else {
> +		ret = 0;
> +unref:
> +		i915_gem_object_put_unlocked(obj);
> +	}
> +
>  	return ret;
>  }
>  
> -- 
> 2.8.1
> 

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