i have created two rtos task which will read data from USB. In this case, the RTOS task is polling every 7 ms, Hwo can i reduce this to get the data in micro seconds?

Can you please be more specific as to what your question is as the subject line and content of your post don't seem to match. Are you wanting to switch between tasks at 1us (which is highly undesirable, if even possible), or poll something?

Better avoid this kind of design. Continous microsec response times are pretty hard to achieve reliably even today and you'd need a pretty fast processor. In short is this really required and/or matches the requirements of your USB data source ?

Any action that needs a 1us response time basically needs to be in the ISR, which also limits what it can do. You also need to be sure no higher priority interrupts can block it.

USB ideally has DMA to fetch a packet, and you don't need to do much until you have a packet, and then you don't need us time scale operations.