Quoted from Barry Miles' Many Years From Now:
p.175. PAUL: 'What You're Doing' was a bit of a filler. I think it was a little more mine than John's, but I don't have a very clear recollection, so to be on the safe side I'd put it as 50-50. It doesn't sound like an idea that I remember John offering, so it sounds like a way to get a song started, some of them are just like that. 'Hey, what'cha doing?' You sometimes start a song and hope the best bit will arrive by the time you get to the chorus ... but sometimes that's all you get, and I suspect this was one of them. Maybe it's a better recording than it is a song, some of them are. Sometimes a good recording would enhance the song.
It was the first song in which The Beatles deliberately distorted the tape by overriding the desk, the beginning of a
series of experimental recording techniques which would stretch George Martin's skill and imagination to the utmost and test
EMI's archaic equipment at Abbey Road to the limit.