[Mesa-dev] [RFC] gallium/u_queue: add barrier function

[Rob Clark]

On Mon, Jul 18, 2016 at 4:34 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
> On 18.07.2016 22:25, Rob Clark wrote:
>>
>> Helper to block until all previous jobs are complete.
>> ---
>> So I think this might end up being useful to me in some cases.. but
>> the implementation only works for a single threaded queue (which is
>> all I need).  I could also just put a helper in my driver code.
>>
>> Opinions?
>
>
> What do you need it for? ISTR Marek had a half-finished patch for
> dependencies, maybe that does what you need and is more expressive?

no, I don't think dependencies would really help me..

This issue I'm chancing down is a race condition which, I think,
amounts to we initially flush a batch when we don't think we need to
wait for it to complete, and later get a flush_resource() or a flush()
and realize we did actually need it to complete, but no longer have a
ref to the batch (or it's contained fence)..

BR,
-R

> Cheers,
> Nicolai
>
>
>>
>>   src/gallium/auxiliary/util/u_queue.c | 12 ++++++++++++
>>   src/gallium/auxiliary/util/u_queue.h |  2 ++
>>   2 files changed, 14 insertions(+)
>>
>> diff --git a/src/gallium/auxiliary/util/u_queue.c
>> b/src/gallium/auxiliary/util/u_queue.c
>> index 838464f..861faca 100644
>> --- a/src/gallium/auxiliary/util/u_queue.c
>> +++ b/src/gallium/auxiliary/util/u_queue.c
>> @@ -242,3 +242,15 @@ util_queue_add_job(struct util_queue *queue,
>>      pipe_condvar_signal(queue->has_queued_cond);
>>      pipe_mutex_unlock(queue->lock);
>>   }
>> +
>> +static void dummy_execute(void *job, int thread_index) {}
>> +
>> +/* blocks until all previously queued jobs complete: */
>> +void util_queue_barrier(struct util_queue *queue)
>> +{
>> +   struct util_queue_fence fence;
>> +   util_queue_fence_init(&fence);
>> +   util_queue_add_job(queue, &fence /*dummy*/, &fence, dummy_execute,
>> NULL);
>> +   util_queue_job_wait(&fence);
>> +   util_queue_fence_destroy(&fence);
>> +}
>> diff --git a/src/gallium/auxiliary/util/u_queue.h
>> b/src/gallium/auxiliary/util/u_queue.h
>> index 59646cc..8a22ee0 100644
>> --- a/src/gallium/auxiliary/util/u_queue.h
>> +++ b/src/gallium/auxiliary/util/u_queue.h
>> @@ -85,6 +85,8 @@ void util_queue_add_job(struct util_queue *queue,
>>
>>   void util_queue_job_wait(struct util_queue_fence *fence);
>>
>> +void util_queue_barrier(struct util_queue *queue);
>> +
>>   /* util_queue needs to be cleared to zeroes for this to work */
>>   static inline bool
>>   util_queue_is_initialized(struct util_queue *queue)
>>
>