How performance is calculated on a tournament?

I notice that sometimes the second place on a tournament have an higher performance rating than the first place, someone knows about how it is calculated?

eh, Im not sure, but i think that performance is calculated by R (opponent's rating) + 500 if you win, and R - 500 if you lose and then you average it

yup. case closed

Case opened again. Why does berserk grant an extra point?

Give up half your time in the game for the possibility of gaining an extra point. It's an aggressive gamble.