[seL4] seL4 IPC SMP

HI, I have question about IPC on SMP. I ran sel4bench on sabre lite(i.mx6, arm v7) which SMP is on. Sabre lite has 4 cores. I supposed that SMP improved IPC performances. But results were not. seL4_CALL SMP on 504 SMP off 336 Would you give me reason why these results are happened?