OS Scheduling when USB communication is in progress

Hi All,
I developed one C program which continuosaly doing a loopback from my USB de
vice.

Initially i read 1 bytes from the device and imidiately i am writting 1070 b
ytes to the device. I am doing this step for 100000 time.

My program uses our USB IP and driver and dll,that are also devloped by us. 
I ported USB 2.0 IP on ALtera(FPGA) NIOS II 32- bit cpu. In that i wrote C c
ode which does same as HOST. write 1 bytes and read 1070 bytes. As i wrote.

Now in NIOS II i added performance counter which will give me total cycles d
uring one operation. 1 operation means 1 complete read and write. I am repea
ting this up to 100000 time.

Using Performance counter i am getting cycles for the 1 transaction and i st
ored it in one memory location. After complition of 100000 times i print all
 transaction cycle detail. In that i found that every specific interval i am
 getting spikes of 35-40 ms. So i ran my code in high priority and i get les
s spikes and spikes are of 10-15ms of  size. After that i ran my code in rea
l application mode so i got every transaction below 1 ms. But some time my O
S was crashing because of real priority. I changes process priority using Ta
sk Manager. 

So my question is that why EHCI not firing token very fast. I check my devic
e with USB Analyzer and it is capable of delievering fast token from the hos
t but when i analyze the signals coming from EHCI i found that during spikes
 host controller does not sending any tokes to device and my device is in wa
it mode. I need to solve this issue. Why HOST wait for some time even device
 is completely ready for transaction. IS this the problem of OS scheduling?

I need any how 7 mbps speed on an average during 1 transaction. Below this i
 will lost my data, If any one having any idea then please let me know as so
on as possible.

Regards,
slsnios