predictor: rebatch tasks to increase CUDA throughput…

- depending on model type (i.e. size), configure target
  batch sizes
- after receiving a prediction task for some model,
  look up target batch size, then try to retrieve arrays
  from follow-up tasks for the same model on the task queue;
  stop when either no tasks are immediately available or
  when the combined batch size (input batch size * number of tasks)
  reaches the target
- push back tasks for other models to the queue
- rebatch: read all shared arrays, concatenate them along axis 0,
  map respective job ids they came from
- predict on new (possibly larger) batch
- split result along axis 0 into number of jobs
- send each result along with its jobid to task queue

src/eynollah/predictor.py

@@ -109,29 +109,80 @@ class Predictor(mp.context.SpawnProcess):
         while not self.stopped.is_set():
             close_all()
             try:
-                jobid, model, shared_data = self.taskq.get(timeout=1.1)
+                TIMEOUT = 4.5 # 1.1 too is greedy - not enough for rebatching
+                jobid, model, shared_data = self.taskq.get(timeout=TIMEOUT)
             except mp.queues.Empty:
                 continue
             try:
-                model = self.model_zoo.get(model)
+                # up to what batch size fits into small (8GB) VRAM?
+                # (notice we are not listing _resized/_patched models here,
+                #  because here inputs/outputs will have varying shapes)
+                REBATCH_SIZE = {
+                    # small models (448x448)...
+                    "col_classifier": 4,
+                    "page": 4,
+                    "binarization": 5,
+                    "enhancement": 5,
+                    "reading_order": 5,
+                    # medium size (672x672)...
+                    "textline": 3,
+                    # large models...
+                    "table": 2,
+                    "region_1_2": 2,
+                    "region_fl_np": 2,
+                    "region_fl": 2,
+                }.get(model, 1)
+                loaded_model = self.model_zoo.get(model)
                 if not len(shared_data):
                     #self.logger.debug("getting '%d' output shape of model '%s'", jobid, model)
-                    result = model.output_shape
+                    result = loaded_model.output_shape
+                    self.resultq.put((jobid, result))
+                    #self.logger.debug("sent result for '%d': %s", jobid, result)
                 else:
-                    #self.logger.debug("predicting '%d' with model '%s': ", jobid, model, shared_data)
-                    with ndarray_shared(shared_data) as data:
-                        result = model.predict(data, verbose=0)
+                    other_tasks = [] # other model, put back on q
+                    model_tasks = [] # same model, for rebatching
+                    model_tasks.append((jobid, shared_data))
+                    batch_size = shared_data['shape'][0]
+                    while (not self.taskq.empty() and
+                           # climb to target batch size
+                           batch_size * len(model_tasks) < REBATCH_SIZE):
+                        jobid0, model0, shared_data0 = self.taskq.get()
+                        if model0 == model and len(shared_data0):
+                            # add to our batch
+                            model_tasks.append((jobid0, shared_data0))
+                        else:
+                            other_tasks.append((jobid0, model0, shared_data0))
+                    if len(other_tasks):
+                        self.logger.debug("requeuing %d other tasks", len(other_tasks))
+                    for task in other_tasks:
+                        self.taskq.put(task)
+                    if len(model_tasks) > 1:
+                        self.logger.debug("rebatching %d %s tasks of batch size %d", len(model_tasks), model, batch_size)
+                    with ExitStack() as stack:
+                        data = []
+                        jobs = []
+                        for jobid, shared_data in model_tasks:
+                            #self.logger.debug("predicting '%d' with model '%s': ", jobid, model, shared_data)
+                            jobs.append(jobid)
+                            data.append(stack.enter_context(ndarray_shared(shared_data)))
+                        data = np.concatenate(data)
+                        result = loaded_model.predict(data, verbose=0)
+                    results = np.split(result, len(jobs))
                     #self.logger.debug("sharing result array for '%d'", jobid)
                     with ExitStack() as stack:
-                        # we don't know when the result will be received,
-                        # but don't want to wait either, so 
-                        result = stack.enter_context(share_ndarray(result))
-                        closing[jobid] = stack.pop_all()
+                        for jobid, result in zip(jobs, results):
+                            # we don't know when the result will be received,
+                            # but don't want to wait either, so track closing
+                            # context per job, and wait for closable signal
+                            # from client
+                            result = stack.enter_context(share_ndarray(result))
+                            closing[jobid] = stack.pop_all()
+                            self.resultq.put((jobid, result))
+                            #self.logger.debug("sent result for '%d': %s", jobid, result)
             except Exception as e:
-                self.logger.error("prediction '%d' failed: %s", jobid, e.__class__.__name__)
+                self.logger.error("prediction failed: %s", e.__class__.__name__)
                 result = e
-            self.resultq.put((jobid, result))
-            #self.logger.debug("sent result for '%d': %s", jobid, result)
+                self.resultq.put((jobid, result))
         close_all()
         #self.logger.debug("predictor terminated")