What is kernel bypass and why is it used in high-performance systems?

Kernel bypass allows user-space applications to access hardware directly, avoiding kernel overhead (system calls, context switches, copying). Techniques: DPDK (Data Plane Development Kit) for networking - polls NICs in user space, achieves millions of packets/sec; RDMA (Remote Direct Memory Access) for zero-copy network transfers; SPDK for storage. Trade-offs: loses kernel protection/isolation, application must handle everything, dedicated cores/resources. Used in HFT, NFV, high-performance storage.