Re: [PATCH 1/2] dma-buf/fence: add fence_collection fences

Christian König
2016-05-19T07:47:11Z

Am 19.05.2016 um 00:57 schrieb Chris Wilson:
> On Wed, May 18, 2016 at 05:59:52PM -0300, Gustavo Padovan wrote:
>> +static void collection_check_cb_func(struct fence *fence, struct fence_cb *cb)
>> +{
>> + struct fence_collection_cb *f_cb;
>> + struct fence_collection *collection;
>> +
>> + f_cb = container_of(cb, struct fence_collection_cb, cb);
>> + collection = f_cb->collection;
>> +
>> + if (atomic_dec_and_test(&collection->num_pending_fences))
>> + fence_signal(&collection->base);
>> +}
>> +
>> +static bool fence_collection_enable_signaling(struct fence *fence)
>> +{
>> + struct fence_collection *collection = to_fence_collection(fence);
>> + int i;
>> +
>> + for (i = 0 ; i < collection->num_fences ; i++) {
>> + if (fence_add_callback(collection->fences[i].fence,
>> + &collection->fences[i].cb,
>> + collection_check_cb_func)) {
>> + atomic_dec(&collection->num_pending_fences);
>> + }
>> + }
> We don't always have a convenient means to preallocate an array of
> fences to use. Keeping a list of fences in addition to the array would
> be easier to user in many circumstances.

I agree that there is use for such an implementation as well, but as
mentioned in the last review cycle we intentionally chose an array
instead of a more complex implementation here.

This way the array can be passed to function like
fence_wait_any_timeout() as well.

I also suggested to rename it to fence_array to make that difference
clear and allow for another implementation to live side by side with this.

My crux at the moment is that I need both for the amdgpu driver, an
array based implementation and a collection like one.

Gustavo would you mind if I take your patches and work a bit on this?

>
> Just means we need a
>
> struct fence_collection_entry {
> struct fence *fence;
> struct list_head link;
> };
>
> int fence_collection_add(struct fence *_collection,
> struct fence *fence)
> {
> struct fence_collection *collection =
> to_fence_collection(_collection);
> struct fence_collection_entry *entry;
>
> entry = kmalloc(sizeof(*entry), GFP_KERNEL);
> if (!entry)
> return -ENOMEM;
>
> entry->fence = fence_get(fence);
> list_add_tail(&entry->link, &collection->fence_list);
> atomic_inc(&collection->num_pending_fences);
>
> return 0;
> }
>
> and a couple of list iterations as well as walking the arrays.
>
> (This fence_collection_add() needs to be documented to only be valid
> from the constructing thread before the fence is sealed for export/use.)

As suggested by Daniel as well I would prefer that the the array
implementation only gets the fences as already filled array in the
constructor. This is much more fail save.

Christian.

> -Chris
>