One is passive and one is active. The first one is the active one--it emphasizes that the action has been done by the subject (the teacher). The second one is passive and emphasizes the object (the homework). The sentences mean exactly the same thing, but you can choose which one is more appropriate based on context.

The end result is the same, but in the first sentence you are talking about the teacher, and in the second you are talking about the homework. In the second sentence, if you don't know (or don't want to say) who marked the homework, then "All the homework has been marked" is still a complete sentence.

They have the same meaning but the second sentence is written in the passive voice.

They have the same meaning.