Merge pull request #2925 from yichengq/doc-gomaxprocs

docs: document cpu cores deployment

Documentation/admin_guide.md

@@ -209,3 +209,11 @@ If the request times out, it indicates two possibilities:
 2. the majority of the cluster is not functioning.
 
 If timeout happens several times continuously, administrators should check status of cluster and resolve it as soon as possible.
+
+### Best Practices
+
+#### Maximal OS threads
+
+By default, etcd uses the default configuration of the Go 1.4 runtime, which means that at most one operating system thread will be used to execute code simultaneously. (Note that this default behavior [may change in Go 1.5](https://docs.google.com/document/d/1At2Ls5_fhJQ59kDK2DFVhFu3g5mATSXqqV5QrxinasI/edit)).
+
+When using etcd in heavy-load scenarios on machines with multiple cores it will usually be desirable to increase the number of threads that etcd can utilize. To do this, simply set the environment variable `GOMAXPROCS` to the desired number when starting etcd. For more information on this variable, see the Go [runtime](https://golang.org/pkg/runtime) documentation.