Give some stream of consciousness and then the answer. "Who You Love" is a song written and performed by John Mayer and Katy Perry for Mayer's sixth studio album, Paradise Valley (2013). It appears as the sixth song on the album and is the third single from the record. Mayer co-produced the song with Don Was and released it as an Internet download on August 12, 2013. Lyrically, "Who You Love" is a ballad about accepting falling in love with someone, on the theory that "you love who you love". The song has been praised by critics and has received mostly positive reviews.

Based on this passage, who sings with john mayer on who you love?
To answer this question, we should know that: "Who You Love" is a song written and performed by John Mayer and Katy Perry for Mayer's sixth studio album, Paradise Valley (2013).
Therefore, the answer is Katy Perry.