Who Knocked Up The Knockers-Up?

As I was sleepy before we were far away from the prison-ship, Joe took me on his back again and carried me home. 

He must have had a tiresome journey of it, for Mr Wopsle, being knocked up, was in such a very bad temper that if the Church had been thrown open, he would probably have excommunicated the whole expedition, beginning with Joe and myself.

Given the modern vernacular, one might be forgiven for looking askance at Dickens' use of "knocked up" in reference to a "Mr." — but that's because the vernacular changes.

You see, for all of human history, people awoke pretty much when they awoke. For the last century or so, people awoke when they set their alarm to wake them. But there was a brief period in between, as the Industrial Revolution was well under way and people were obligated to be places (e.g., the factory) at a certain hour, but gas and electric lighting made staying awake well into the night more convenient and enjoyable, and the alarm clock was not yet cheaply available to the mass market, when there existed the profession of "knocker-upper".

Knockers-upper were people who were paid to go around and knock on the doors or windows of their customers, in order to wake them at a certain time.

The question is, who knocked-up the knockers-upper?

Or, as a tongue-twister of the time put it,

We had a knocker-up, and our knocker-up had a knocker-up

And our knocker-up's knocker-up didn't knock our knocker up 

So our knocker-up didn't knock us up 

'Cos he's not up.