A processor can offer a number of cache-related features to enable easy implementation of multicore systems. L1 cache coherence is critical for multicore Symmetric Multi-Processing (SMP). When two or more CPUs access the same memory, some mechanism must keep the cached data coherent to prevent the CPUs from independently modifying the same data. Maintaining this coherence in software is difficult and consumes numerous clock cycles, so cache-coherent processors implement this mechanism in hardware by using snooping to monitor all L1 caches for read and write operations and keep the cached data coherent with the data in the other caches.
Additionally, an I/O coherency unit that keeps input/output traffic coherent with the L1 caches automatically handles complex bookkeeping. For example, when an I/O device modifies data in one core's L1 cache, the I/O coherency unit updates the other L1 caches, removing the need for the application programmer to focus on these details.
Another way to boost performance is to design a processor with a user-configurable level-two (L2) cache to reduce main-memory accesses. An L2 cache can include several features that ensure high performance while consuming minimal power. For example, an L2 cache designed to run at the same clock frequency as the processor and shared by all the cores in a multicore cluster ensures that the L2 cache can keep up with the CPUs. In addition, a cache tightly connected with the core through a separate low-latency bus avoids AXI bus traffic on the data paths between the CPU cores and the L2 cache, further improving performance.
Processors that offer a high degree of configurability can offer excellent power and performance benefits. Besides being able to configure the L2 cache's clock speed, memory size, and AXI interfaces, designers using configurable processors can customize the core and make use of different sleep modes to save power. When chip designers implement the L2 cache, they can also select higher-density SRAMs to reduce power consumption and die area, although performance will suffer a bit.