Apple Inc.

Perumal R Subramoniam

Brian P Lilly

Hari Kannan

Pradeep Kanapathipillai

Gerard Richard Williams

Mahnaz P Sadoughi-Yarandi

Sandeep Kumar Gupta

Prashant Jain

Gerard R Williams Iii

Hari S Kannan

A system and method for efficiently handling data selected for eviction in a computing system. In various embodiments, a computing system includes one or more processors, a system memory, and a victim cache. The cache controller of a particular cache in a cache memory subsystem includes an allocator for determining whether to allocate data evicted from the particular cache into the victim cache. The data fetched into the first cache includes data fetched to service miss requests, which includes demand requests and prefetch requests. To determine whether to allocate, the allocator determines whether a usefulness of data fetched into the particular cache exceeds a threshold. If so, the evicted data is stored in the victim cache. If not, the evicted data bypasses the victim cache. Data determined to be accessed by a processor is deemed to be of a higher usefulness.

Victim allocations in shared system cache

An apparatus for processing cache requests in a computing system is disclosed. The apparatus may include a pending request buffer and a control circuit. The pending request buffer may include a plurality of buffer entries. The control circuit may be coupled to the pending request buffer and may be configured to receive a request for a first cache line from a pre-fetch engine, and store the received request in an entry of the pending request buffer. The control circuit may be further configured to receive a request for a second cache line from a processor, and store the request received from the processor in the entry of the pending request buffer in response to a determination that the second cache line is the same as the first cache line.

Cache pre-fetch merge in pending request buffer

Systems, methods, and apparatuses for implementing selective victimization to reduce power and utilized bandwidth in a multi-level cache hierarchy. Each set of an upper-level cache includes a counter that keeps track of the number of times the set was accessed. These counters are periodically decremented by another counter that tracks the total number of accesses to the cache. If a given set counter is below a certain threshold value, clean victims are dropped from this given set instead of being sent to a lower-level cache. Also, a separate counter is used to track the total number of outstanding requests for the cache as a proxy for bus-bandwidth in order to gauge the total amount of traffic in the system. The cache will implement selective victimization whenever there is a large amount of traffic in the system.

Selective victimization in a multi-level cache hierarchy

Systems, methods, and apparatuses for reducing writes to the data array of a cache. A cache hierarchy includes one or more L1 caches and a L2 cache inclusive of the L2 cache(s). When a request from the L1 cache misses in the L2 cache, the L2 cache sends a fill request to memory. When the fill data returns from memory, the L2 cache delays writing the fill data to its data array. Instead, this cache line is written to the L1 cache and a clean-evict bit corresponding to the cache line is set in the L1 cache. When the L1 cache evicts this cache line, the L1 cache will write back the cache line to the L2 cache even if the cache line has not been modified.

Delaying cache data array updates

Processors and methods for coordinating prefetch units at multiple cache levels. A single, unified training mechanism is utilized for training on streams generated by a processor core. Prefetch requests are sent from the core to lower level caches, and a packet is sent with each prefetch request. The packet identifies the stream ID of the prefetch request and includes relevant training information for the particular stream ID. The lower level caches generate prefetch requests based on the received training information.

Coordinated prefetching based on training in hierarchically cached processors

Processors and methods for preventing lower level prefetch units from stalling at page boundaries. An upper level prefetch unit closest to the processor core issues a preemptive request for a translation of the next page in a given prefetch stream. The upper level prefetch unit sends the translation to the lower level prefetch units prior to the lower level prefetch units reaching the end of the current page for the given prefetch stream. When the lower level prefetch units reach the boundary of the current page, instead of stopping, these prefetch units can continue to prefetch by jumping to the next physical page number provided in the translation.

Prefetching across page boundaries in hierarchically cached processors

Systems, processors, and methods for keeping uncacheable data coherent. A processor includes a multi-level cache hierarchy, and uncacheable load memory operations can be cached at any level of the cache hierarchy. If an uncacheable load misses in the L2 cache, then allocation of the uncacheable load will be restricted to a subset of the ways of the L2 cache. If an uncacheable store memory operation hits in the L1 cache, then the hit cache line can be updated with the data from the memory operation. If the uncacheable store misses in the L1 cache, then the uncacheable store is sent to a core interface unit. Multiple contiguous store misses are merged into larger blocks of data in the core interface unit before being sent to the L2 cache.

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San Jose, CA, United States of America

Perumal R Subramoniam