6. As shown in Figure 2, in rectangle $A B C D$, it is known that the diagonal length is 2, and $\angle 1=\angle 2=\angle 3=\angle 4$. Then the perimeter of quadrilateral $E F G H$ is ( ).
(A) $2 \sqrt{2}$
(B) 4
(C) $4 \sqrt{2}$
(D) 6