Armor: How effective was Chainmail

[Lothia]

Ave Civitas,

I was wondering, having watched movies aplenty, I remember many scenes where a spear or sword penetrated chainmail.
I know there were specially designed narrow-headed arrows designed to penetrate chainmail (crusade period) but just how effective was, and how forceful would a thrust have to be, to penetrate a chainmail cuirass?

Thanks,
Tom