[RELNOTES] [P] Write to TensorBoard every x samples. (keras-team#11152)

* Working on improving tensor flow callbacks

* Adding batch level TensorBoard logging (implementing the `on_batch_end` method to the TensorBoard class

* Interim commit -- added notes.

* Corrected stylistic issues -- brought to compliance w/ PEP8

* Added the missing argument in the test suite.

* Added the possibility to choose how frequently tensorboard should log
the metrics and losses.

* Fixed the issue of the validation data not being displayed.

* Fixed the issue about the callback not remembering when was the last
time it wrote to the logs.

* Removed the error check.

* Used update_freq instead of write_step.

* Forgot to change the constructor call.

keras/callbacks.py

@@ -719,6 +719,12 @@ class TensorBoard(Callback):
             input) or list of Numpy arrays (if the model has multiple inputs).
             Learn [more about embeddings]
             (https://www.tensorflow.org/programmers_guide/embedding).
+        update_freq: `'batch'` or `'epoch'` or integer. When using `'batch'`, writes
+            the losses and metrics to TensorBoard after each batch. The same
+            applies for `'epoch'`. If using an integer, let's say `10000`,
+            the callback will write the metrics and losses to TensorBoard every
+            10000 samples. Note that writing too frequently to TensorBoard
+            can slow down your training.
     """
 
     def __init__(self, log_dir='./logs',
@@ -730,7 +736,8 @@ def __init__(self, log_dir='./logs',
                  embeddings_freq=0,
                  embeddings_layer_names=None,
                  embeddings_metadata=None,
-                 embeddings_data=None):
+                 embeddings_data=None,
+                 update_freq='epoch'):
         super(TensorBoard, self).__init__()
         global tf, projector
         try:
@@ -769,6 +776,13 @@ def __init__(self, log_dir='./logs',
         self.embeddings_metadata = embeddings_metadata or {}
         self.batch_size = batch_size
         self.embeddings_data = embeddings_data
+        if update_freq == 'batch':
+            # It is the same as writing as frequently as possible.
+            self.update_freq = 1
+        else:
+            self.update_freq = update_freq
+        self.samples_seen = 0
+        self.samples_seen_at_last_write = 0
 
     def set_model(self, model):
         self.model = model
@@ -968,6 +982,13 @@ def on_epoch_end(self, epoch, logs=None):
 
                     i += self.batch_size
 
+        if self.update_freq == 'epoch':
+            index = epoch
+        else:
+            index = self.samples_seen
+        self._write_logs(logs, index)
+
+    def _write_logs(self, logs, index):
         for name, value in logs.items():
             if name in ['batch', 'size']:
                 continue
@@ -978,12 +999,20 @@ def on_epoch_end(self, epoch, logs=None):
             else:
                 summary_value.simple_value = value
             summary_value.tag = name
-            self.writer.add_summary(summary, epoch)
+            self.writer.add_summary(summary, index)
         self.writer.flush()
 
     def on_train_end(self, _):
         self.writer.close()
 
+    def on_batch_end(self, batch, logs=None):
+        if self.update_freq != 'epoch':
+            self.samples_seen += logs['size']
+            samples_seen_since = self.samples_seen - self.samples_seen_at_last_write
+            if samples_seen_since >= self.update_freq:
+                self._write_logs(logs, self.samples_seen)
+                self.samples_seen_at_last_write = self.samples_seen
+
 
 class ReduceLROnPlateau(Callback):
     """Reduce learning rate when a metric has stopped improving.

tests/keras/test_callbacks.py

@@ -550,7 +550,8 @@ def make_model():
     assert not tmpdir.listdir()
 
 
-def test_TensorBoard(tmpdir):
+@pytest.mark.parametrize('update_freq', ['batch', 'epoch', 9])
+def test_TensorBoard(tmpdir, update_freq):
     np.random.seed(np.random.randint(1, 1e7))
     filepath = str(tmpdir / 'logs')
 
@@ -588,7 +589,8 @@ def callbacks_factory(histogram_freq, embeddings_freq=1):
                                       embeddings_freq=embeddings_freq,
                                       embeddings_layer_names=['dense_1'],
                                       embeddings_data=X_test,
-                                      batch_size=5)]
+                                      batch_size=5,
+                                      update_freq=update_freq)]
 
     # fit without validation data
     model.fit(X_train, y_train, batch_size=batch_size,