add EI documentation (#733)

* add EI documentation

* fix pmd rules

Change-Id: Ieee5577c26f6df2843781f8f9180de35069a5de3

docs/mkdocs.yml

@@ -84,6 +84,7 @@ nav:
  - Overview: 'mxnet/README.md'
  - Import Gluon Model: 'docs/mxnet/how_to_convert_your_model_to_symbol.md'
  - Load a MXNet Model: 'jupyter/load_mxnet_model.ipynb'
+ - Backend Optimizer for MXNet: 'docs/mxnet/mxnet_backend_optimizer.md'
  - Modules:
  - MXNet Engine: 'mxnet/mxnet-engine/README.md'
  - MXNet Model Zoo: 'mxnet/mxnet-model-zoo/README.md'

docs/mxnet/mxnet_backend_optimizer.md

@@ -0,0 +1,33 @@
+# Custom backend optimizer support on Apache MXNet
+
+Apache MXNet currently implemented a method that allowing third-party
+backend optimizer to accelerate the inference result. DJL currently
+also exposed this functionality through the `MxOptimizeFor` option
+of the Criteria.
+
+```
+.optOption("MxOptimizeFor", "optimizer_name")
+```
+
+After a name is passed, DJL will try to find the party library from
+ the environment variable called `MXNET_EXTRA_LIBRARY_PATH`. Users are required to
+set this environment variable to locate the library. After that, you should see the messages from the inference to see if the library is enabled.
+
+Here is a list of supporting backend optimizers:
+
+## AWS [Elastic Inference Accelerator](https://docs.aws.amazon.com/elastic-inference/latest/developerguide/what-is-ei.html) (EIA)
+
+Currently, you can use EIA library for DJL on all EI enabled instance.
+
+You can follow the instruction to start your EI application with DJL:
+
+```
+> https://docs.aws.amazon.com/elastic-inference/latest/developerguide/ei-mxnet.html
+```
+
+Currently, the EI logging is disabled. For debugging purpose, you can enable that through
+setting the `MXNET_EXTRA_LIBRARY_VERBOSE` environment variable:
+
+```
+export MXNET_EXTRA_LIBRARY_VERBOSE=true
+```

mxnet/mxnet-engine/src/main/java/ai/djl/mxnet/engine/MxEngine.java

@@ -57,9 +57,10 @@ static Engine newInstance() {
 
  // load extra MXNet library
  String paths = System.getenv("MXNET_EXTRA_LIBRARY_PATH");
- boolean extraLibVerbose =
- System.getenv().containsKey(MXNET_EXTRA_LIBRARY_VERBOSE)
- && System.getenv(MXNET_EXTRA_LIBRARY_VERBOSE).equals("true");
+ boolean extraLibVerbose = false;
+ if (System.getenv().containsKey(MXNET_EXTRA_LIBRARY_VERBOSE)) {
+ extraLibVerbose = Boolean.parseBoolean(System.getenv(MXNET_EXTRA_LIBRARY_VERBOSE));
+ }
  if (paths != null) {
  String[] files = paths.split(",");
  for (String file : files) {