Small pleasure being interrupted by mostly boring programmer (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Small pleasure being interrupted by most boring programmer S (=small, in sizes) + [ DUL <l> (=boring; “most” means last letter is dropped) in CHEER (=pleasure, entertainment)]; Peter and the Wolf is a symphonic tale for children composed by the Russian Sergei Prokofiev in 1936