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The IBM z13 processor cache subsystem

The IBM z13™ system introduces many new innovative concepts in building a high-performance modular and scalable symmetrical multiprocessing (SMP) system, comprising up to 192 multithreaded processors that span eight system processing nodes. The z13 uses new socket packaging technology, changing from multichip modules (MCMs) to single-chip modules (SCMs). This enables the modularity and scalability of a large distributed SMP system and led to the development of new techniques in several important performance areas. For the cache hierarchy, the inclusivity management policy is optimized between the third-level and the fourth-level shared caches to improve overall cache-bit efficiency, effectively making the fourth-level cache larger to reduce the impact of increased chip socket-to-socket access latencies. The system bus management is enhanced such that multiple data transfers can be simultaneously overlapped on an interface to reduce wait times on critical data when these buses are highly utilized. With the amount of caches on both the Central Processor (CP) and System Controller (SC) chips, several major improvements were made for array macro resiliency to improve overall system availability. These and other major design updates in the latest mainframe processor cache subsystem are described in this paper.