How does cache coherence impact multithreading?

What is cache coherence and why is it important in multithreading?

Cache coherence refers to the consistency of data stored in local caches of a shared resource. In multithreading, it's crucial because multiple threads may access and modify shared data, leading to potential inconsistencies if caches are not synchronized.

How does cache coherence affect performance in multithreaded applications?

Cache coherence can significantly impact performance. If caches are not coherent, threads may spend time waiting for data to be updated, leading to increased latency and reduced throughput. Efficient cache coherence protocols help minimize these delays.

What are some common cache coherence protocols?

Some common cache coherence protocols include MESI (Modified, Exclusive, Shared, Invalid), MOESI, and MSI. Each protocol has its own method for maintaining consistency across caches.

Can you explain the MESI protocol in detail?

Sure! The MESI protocol uses four states for cache lines: Modified, Exclusive, Shared, and Invalid. It ensures that any changes made to a cache line are propagated to other caches, maintaining coherence while optimizing performance.