Probably the most primal and earth-shaking performance you’ll see at this year’s fest is that of Andy Serkis as the 1970s English rocker Ian Dury, who helped popularize the phrase and is the subject of the Mat Whitecross film “Sex & Drugs & Rock & Roll.’ The film, which has two performances left (buy tickets here), makes the most of a cagey, curmudgeonly, full-throated and fully roguish performance by Serkis (who has already nabbed a BAFTA nomination for his work) in a film that, like this year’s “The Runaways,” is about a rock act that you may not have heard of. Unlike “The Runaways,” though, which was entertaining but quickly fell into cliche, “Sex & Drugs” has a fascinating figure at its core. Dury started out in a Dickensian novel — as a wee lad he was stricken with polio that permanently wasted his left side — and leveraged his anger to a position in 1970s rock, with a sort of music-hall or cabaret twist. Dury also had a barbed wit, which he deployed as a weapon, and a love of wordplay. Serkis’s Dury staggers and swaggers aggressively through the movie delivering raspy bons mots (“Moral compass? I’m an entertainer, not Christopher Bleeding Columbus”) while annoying his wife (who gives birth while Ian and his boys the Blockheads loudly practice in a nearby room) and taking a mistress (Naomie Harris) but attracting the approval of his adolescent son Baxter, who at first is disgusted by his father but slowly starts to imitate him as the film goes on. Colorfully realized animation and stark flashbacks to Dury’s childhood, when his father (Ray Winstone) taught him to always keep picking himself up, flesh out a figure who may not have been seminal (none of his herky-jerky songs was a hit in the US and indeed they didn’t much deserve to be) but, in his disregard for self-pity and in his impish imagination, proves more than worthy of our attention.