[PATCH 01/13] drm: execution context for GEM buffers v4

[Thomas Hellström (Intel)]

On 5/4/23 13:51, Christian König wrote:
> This adds the infrastructure for an execution context for GEM buffers
> which is similar to the existing TTMs execbuf util and intended to replace
> it in the long term.
>
> The basic functionality is that we abstracts the necessary loop to lock
> many different GEM buffers with automated deadlock and duplicate handling.
>
> v2: drop xarray and use dynamic resized array instead, the locking
>      overhead is unecessary and measurable.
> v3: drop duplicate tracking, radeon is really the only one needing that.
> v4: fixes issues pointed out by Danilo, some typos in comments and a
>      helper for lock arrays of GEM objects.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
...
> +/**
> + * struct drm_exec - Execution context
> + */
> +struct drm_exec {
> +	/**
> +	 * @interruptible: If locks should be taken interruptible
> +	 */
> +	bool			interruptible;
> +
> +	/**
> +	 * @ticket: WW ticket used for acquiring locks
> +	 */
> +	struct ww_acquire_ctx	ticket;
> +
> +	/**
> +	 * @num_objects: number of objects locked
> +	 */
> +	unsigned int		num_objects;
> +
> +	/**
> +	 * @max_objects: maximum objects in array
> +	 */
> +	unsigned int		max_objects;
> +
> +	/**
> +	 * @objects: array of the locked objects
> +	 */
> +	struct drm_gem_object	**objects;

Hi, Christian. Did you consider using a list here with links embedded in 
gem objects, now that only locked objects are to be put on the list / array.

That should work as only the process owning the lock may access the list 
link. Apart from getting rid of reallocing this is beneficial for the 
more general types of ww transactions that are used by i915 (and to a 
minor extent xe as well, I think).

In those cases we would want to unlock a temporary held object within 
the while_not_all_locked() loop and would then have to search the entire 
array for the correct pointer. Instead one could just remove it from the 
list of locked objects.

Thanks,

Thomas