Former "Smallville" star Allison Mack couldn't wait to start serving her prison term ... or so it seems, 'cause she showed up more than 2 weeks early to begin serving her sentence.
Allison reported to the facility Monday, according to the Federal Correctional Institution in Dublin, CA. She was supposed to begin serving her sentence on September 29.
Mack was sentenced to 3 years in prison after pleading guilty to one count of racketeering and one count of racketeering conspiracy in her highly publicized sex cult case. She recruited and directed women to have sex with the leader of the cult.
After her release ... Allison will be on supervised release for another 3 years.