Carry out, when through the questionnaire (7)
I believe the answer is:
Here is my best explanation:
'carry out' is the definition.
(performing is a kind of carrying out)
'through the questionnaire' is the wordplay.
'through' becomes 'per' (I've seen this before).
'the questionnaire' becomes 'form' (I can't explain this - if you can you should give a lot more credence to this answer).
'when' is the link.
(Other definitions for perform that I've seen before include "Do - accomplish - act", "Stage", "Act - accomplish", "act on stage", "Act in play or film", "Carry out, accomplish", "Carry out (action)", "seen to make a profit?", "Act or execute" and "Carry out; act".)