Apple Inc.

Other

Brian P Lilly

Ramesh B Gunna

Hari Kannan

Harshavardhan Kaushikkar

James Vash

Mahnaz P Sadoughi-Yarandi

Gerard Richard Williams

Perumal R Subramoniam

Sukalpa Biswas

Sridhar Subramanian

Per Hakan Hammarlund

Krishna C Potnuru

Hao Chen

Pradeep Kanapathipillai

Andrew J Beaumont-Smith

Gaurav Garg

Prashant Jain

Jason M Kassoff

Lital Levy-Rubin

Steven R Hutsell

Perumal R Subramonium

Sandeep Kumar Gupta

Gurjeet S Saund

Wei-Han Lien

David L Lampert

Stephen J Briggs

Edward William Cler

Daniel David Horein

Benjamin Berton Rund

Manu Gulati

Tse-Yu Yeh

Shinye Shiu

Peter J Bannon

Aditya Kesiraju

Derek R Kumar

Shih-Chieh Wen

Tyler J Huberty

Ran A Chachick

Rajdeep L Bhuyar

Jaidev Prasad Patwardhan

Robert Gries

Erik P Machnicki

Srinivasa Rangan Sridharan

Benjamin K Dodge

Michael Bekerman

Muditha Kanchana

Kevin C Wong

Chandan Shantharaj

Sridhar Kotha

Sahil Kapoor

Helen Huang

Gerard R Williams Iii

Hari S Kannan

Sridhar P Subramanian

A system may include multiple coherent agents, where a given coherent agent includes one or more caches configured to cache data. Memory controller circuitry may control one or more memory circuits from which the one or more caches are configured to cache data and maintain a directory that tracks which of the multiple coherent agent circuits is caching copies of a plurality of cache blocks and states of the cached copies in the multiple coherent agent circuits. A first agent may transmit a first request for a first cache block. The first agent may store, in request buffer circuitry, information corresponding to the first request then detect a second snoop from a second agent circuit to the first cache block. The first agent may absorb the second snoop, including to store information corresponding to the second snoop with the information corresponding to the first request in the request buffer circuitry.

Scalable cache coherency protocol

A cache may include multiple request handling pipes, each of which may further include multiple request buffers, for storing device requests from one or more processors to one or more devices. Some of the device requests may require to be sent to the devices according to an order. For a given one of such device requests, the cache may select a request handling pipe, based on an address indicated by the device request, and select a request buffer, based on the available entries of the request buffers of the selected request handling pipe, to store the device request. The cache may further use a first-level and a second-level token stores to track and maintain the device requests in order when transmitting the device requests to the devices.

Request ordering in a cache

A scalable cache coherency protocol for system including a plurality of coherent agents coupled to one or more memory controllers is described. The memory controller may implement a precise directory for cache blocks from the memory to which the memory controller is coupled. Multiple requests to a cache block may be outstanding, and snoops and completions for requests may include an expected cache state at the receiving agent, as indicated by a directory in the memory controller when the request was processed, to allow the receiving agent to detect race conditions. In an embodiment, the cache states may include a primary shared and a secondary shared state. The primary shared state may apply to a coherent agent that bears responsibility for transmitting a copy of the cache block to a requesting agent. In an embodiment, at least two types of snoops may be supported: snoop forward and snoop back.

A variable latency cache memory is disclosed. A cache subsystem includes a pipeline control circuit configured to initiate cache memory accesses for data. The cache subsystem further includes a cache memory circuit having a data array arranged into a plurality of groups, wherein different ones of the plurality of groups have different minimum access latencies due to different distances from the pipeline control circuit. A plurality of latency control circuits configured to ensure a latency is bounded to a maximum value for a given access to the data array, wherein a given latency control circuit is associated with a corresponding group of the plurality of groups. The latency for a given access may thus vary between a minimum access latency for a group closest to the pipeline control circuit to a maximum latency for an access to the group furthest from the pipeline control circuit.

Variable hit latency cache

A system may include a plurality of processors and a coprocessor. A plurality of coprocessor context priority registers corresponding to a plurality of contexts supported by the coprocessor may be included. The plurality of processors may use the plurality of contexts, and may program the coprocessor context priority register corresponding to a context with a value specifying a priority of the context relative to other contexts. An arbiter may arbitrate among instructions issued by the plurality of processors based on the priorities in the plurality of coprocessor context priority registers. In one embodiment, real-time threads may be assigned higher priorities than bulk processing tasks, improving bandwidth allocated to the real-time threads as compared to the bulk tasks.

Coprocessor context priority

Systems, apparatuses, and methods for performing coherence processing and memory cache processing in parallel are disclosed. A system includes a communication fabric and a plurality of dual-processing pipelines. Each dual-processing pipeline includes a coherence processing pipeline and a memory cache processing pipeline. The communication fabric forwards a transaction to a given dual-processing pipeline, with the communication fabric selecting the given dual-processing pipeline, from the plurality of dual-processing pipelines, based on a hash of the address of the transaction. The given dual-processing pipeline performs a duplicate tag lookup in parallel with a memory cache tag lookup for the transaction. By performing the duplicate tag lookup and the memory cache tag lookup in a parallel fashion rather than in a serial fashion, latency and power consumption are reduced while performance is enhanced.

Parallel coherence and memory cache processing pipelines

Various systems and methods for ensuring real-time snoop latency are disclosed. A system includes a processor and a cache controller. The cache controller receives, via a channel, cache snoop requests from the processor, the snoop requests including latency-sensitive and non-latency sensitive requests. Requests are not prioritized by type within the channel. The cache controller limits a number of non-latency sensitive snoop requests that can be processed ahead of an incoming latency-sensitive snoop requests. Limiting the number of non-latency sensitive snoop requests that can be processed ahead of an incoming latency-sensitive snoop request includes the cache controller determining that the number of received non-latency sensitive snoop requests has reached a predetermined value and responsively prioritizing latency-sensitive requests over non-latency sensitive requests.

Method and apparatus for ensuring real-time snoop latency

A mechanism for evicting a cache line from a cache memory includes first selecting for eviction a least recently used cache line of a group of invalid cache lines. If all cache lines are valid, selecting for eviction a least recently used cache line of a group of cache lines in which no cache line of the group of cache lines is also stored within a higher level cache memory such as the L1 cache, for example. Lastly, if all cache lines are valid and there are no non-inclusive cache lines, selecting for eviction the least recently used cache line stored in the cache memory.

Least recently used mechanism for cache line eviction from a cache memory

A method and apparatus for selectively powering down a portion of a cache memory includes determining a power down condition dependent upon a number of accesses to the cache memory. In response to the detection of the power down condition, selecting a group of cache ways included in the cache memory dependent upon a number of cache lines in each cache way that are also included in another cache memory. The method further includes locking and flushing the selected group of cache ways, and then activating a low power mode for the selected group of cache ways.

Selective cache way-group power down

A method and apparatus for evicting cache lines from a cache memory includes receiving a request from one of a plurality of processors. The cache memory is configured to store a plurality of cache lines, and a given cache line includes an identifier indicating a processor that performed a most recent access of the given cache line. The method further includes selecting a cache line for eviction from a group of least recently used cache lines, where each cache line of the group of least recently used cache lines occupy a priority position less that a predetermined value, and then evicting the selected cache line.

Methods for cache line eviction

Systems and methods for reducing leakage power in a L2 cache within a SoC. The L2 cache is partitioned into multiple banks, and each bank has its own separate power supply. An idle counter is maintained for each bank to count a number of cycles during which the bank has been inactive. The temperature and leaky factor of the SoC are used to select an operating point of the SoC. Based on the operating point, an idle counter threshold is set, with a high temperature and high leaky factor corresponding to a relatively low idle counter threshold, and with a low temperature and low leaky factor corresponding to a relatively high idle counter threshold. When a given idle counter exceeds the idle counter threshold, the voltage supplied to the corresponding bank is reduced to a voltage sufficient for retention of data but not for access.

L2 cache retention mode

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San Francisco, CA, United States of America

Brian P Lilly