There is no way to change "task-core-threads"

I tried to change the value of "task-core-threads" in web admin console to 128, but after restart it is set back to the default value 2. I searched in standalone.xml and didn't found any "128" in it.

Then I guessed and tried to add an attribute "task-core-threads" in the work config xml but that made wildfly fail to start with an error like "worker node doesn't have attribute task-core-threads":

<worker name="default" io-threads="8" task-max-threads="512" task-core-threads="128"/>

So, "task-core-threads" is just a fake? My app server now meets a performance bottleneck for http connections, how to change task-core-threads's value?