This post is contained into the final paper of Matias Vara named “Paralelizacion de Algoritmos Numericos con TORO Kernel” to get the degree on Electronic Engeniering from Universidad de La Plata. These theorical documents help to understand the kernel design.
When a Kernel is designed for a multicore system, the shared memory must be protected of concurrent writing accesses. The memory's protection increments kernel code complexity and decreases operative system's performance. If one or more processors are having access to some data at the same time, mutual exclusion must be realized to protect shared data in multicore systems.
 Paula McKenney: RCU vs. Locking Performance on Different Types of CPUs.