can't reach 1080p30 on dm368

Hi all:

Recently  I try to achieve a stable 1080p30 H.264 performance with DM368  .

the image  is good  When I use ISIF-->DDR-->RSZ-->DDR path.but it only  reach 25fps.

So I change  my path to ISIF-->RSZ-->DDR.it can reach 30fps.but the image we get is terrible.

any guys who know why I can't get the correct image with the ISIF-->RSZ-->DDR path?

Whether there are some other parameters  I need to be modified？

Any suggestions will be helpful.
Thanks