add a new flax example for Bert model inference (#34794)

* add a new example for flax inference cases

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update examples/flax/language-modeling/README.md

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* fix for "make fixup"

---------

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

examples/flax/language-modeling/README.md

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 -->
 
-# Language model training examples
+# Language model training and inference examples
 
 The following example showcases how to train a language model from scratch
 using the JAX/Flax backend.
@@ -542,3 +542,27 @@ python3 -m torch.distributed.launch --nproc_per_node ${NUM_GPUS} run_mlm.py \
     --report_to="tensorboard" \
     --save_strategy="no"
 ```
+
+## Language model inference with bfloat16
+
+The following example demonstrates performing inference with a language model using the JAX/Flax backend.
+
+The example script run_bert_flax.py uses bert-base-uncased, and the model is loaded into `FlaxBertModel`.
+The input data are randomly generated tokens, and the model is also jitted with JAX.
+By default, it uses float32 precision for inference. To enable bfloat16, add the flag shown in the command below.
+
+```bash
+python3 run_bert_flax.py --precision bfloat16
+> NOTE: For JAX Versions after v0.4.33 or later, users will need to set the below environment variables as a \
+> temporary workaround to use Bfloat16 datatype. \
+> This restriction is expected to be removed in future version
+```bash
+export XLA_FLAGS=--xla_cpu_use_thunk_runtime=false
+```
+bfloat16 gives better performance on GPUs and also Intel CPUs (Sapphire Rapids or later) with Advanced Matrix Extension (Intel AMX).  
+By changing the dtype for `FlaxBertModel `to `jax.numpy.bfloat16`, you get the performance benefits of the underlying hardware.
+```python
+import jax
+model = FlaxBertModel.from_pretrained("bert-base-uncased", config=config, dtype=jax.numpy.bfloat16)
+```
+Switching from float32 to bfloat16 can increase the speed of an AWS c7i.4xlarge with Intel Sapphire Rapids by more than 2x.

examples/flax/language-modeling/run_bert_flax.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+import time
+from argparse import ArgumentParser
+
+import jax
+import numpy as np
+
+from transformers import BertConfig, FlaxBertModel
+
+
+parser = ArgumentParser()
+parser.add_argument("--precision", type=str, choices=["float32", "bfloat16"], default="float32")
+args = parser.parse_args()
+
+dtype = jax.numpy.float32
+if args.precision == "bfloat16":
+    dtype = jax.numpy.bfloat16
+
+VOCAB_SIZE = 30522
+BS = 32
+SEQ_LEN = 128
+
+
+def get_input_data(batch_size=1, seq_length=384):
+    shape = (batch_size, seq_length)
+    input_ids = np.random.randint(1, VOCAB_SIZE, size=shape).astype(np.int32)
+    token_type_ids = np.ones(shape).astype(np.int32)
+    attention_mask = np.ones(shape).astype(np.int32)
+    return {"input_ids": input_ids, "token_type_ids": token_type_ids, "attention_mask": attention_mask}
+
+
+inputs = get_input_data(BS, SEQ_LEN)
+config = BertConfig.from_pretrained("bert-base-uncased", hidden_act="gelu_new")
+model = FlaxBertModel.from_pretrained("bert-base-uncased", config=config, dtype=dtype)
+
+
+@jax.jit
+def func():
+    outputs = model(**inputs)
+    return outputs
+
+
+(nwarmup, nbenchmark) = (5, 100)
+
+# warmpup
+for _ in range(nwarmup):
+    func()
+
+# benchmark
+
+start = time.time()
+for _ in range(nbenchmark):
+    func()
+end = time.time()
+print(end - start)
+print(f"Throughput: {((nbenchmark * BS)/(end-start)):.3f} examples/sec")