The measurements for volatile memory access in QNX is taking about 2.5 usec and Linux is about 1 usec.
The measurement in QNX was done using Momentics IDE QNX 6.5 version 4.7.0.

I was trying to optimized this time taken by QNX , any suggestions ?

I used in32 and out32 APIs to perform this test. I wrote a simple test application to execute this APIs for 1000 times 
and took the time measurement.

The Platform used was IMX6DQ clocking at 800 MHz for both Linux and QNX