US 2012/0072671 A1 · PREFETCH STREAM FILTER WITH FIFO ALLOCATION AND STREAM DIRECTION PREDICTION

Abstract

A prefetch filter receives a memory read request having an associated address for accessing data that is stored in a line of memory. An address window is determined that has an address range that encompasses an address space that is twice as large as the line of memory. In response to a determination of in which half the address window includes the requested line of memory, a prefetch direction is to a first direction or to an opposite direction. The prefetch filter can include an array of slots for storing a portion of a next predicted access and determine a memory stream in response to a hit on the array by a subsequent memory request. The prefetch filter FIFO counter cycles through the slots of the array before wrapping around to a first slot of the array for storing a next predicted address portion.

Claims20

Dependent claims

A method for predicting memory streams for memory prefetching in caching systems, comprising:

receiving a memory request having an address used for generating a cache request for addressing a line of memory having a line length of consecutive memory locations;
determining an address window for addressing a length of consecutive memory locations that is twice the line length, wherein the address window is aligned to a power of two and includes the requested line of memory in either an upper half of the address window or a lower half of the address window;
and
setting a prefetch direction for a prefetch operation to a first direction when the requested line of memory is in the upper half of the address window, and setting the prefetch direction to an opposite direction when the requested line of memory is in the upper half of the address window.

1 more element

A digital system, comprising:

a memory including local memory and a lower-level hierarchical memory for storing and retrieving data;
and
a prefetch filter that includes a memory interface that is arranged to receive a memory read request having an associated address that points to a line of memory stored in the lower-level hierarchical memory, wherein the prefetch filter is arranged to determine an address window for addressing a length of consecutive memory locations that is twice the length of the line of memory, wherein the address window is aligned to a power of two and includes the requested line of memory in either an upper half of the address window or a lower half of the address window, and wherein the prefetch filter is arranged to set a prefetch direction for a prefetch operation to an increasing direction when the requested line of memory is in the upper half of the address window, and to set the prefetch direction to a decreasing direction when the requested line of memory is in the upper half of the address window.

A prefetch filter for determining memory streams in caching systems, comprising:

a memory interface that is arranged to receive a memory read request having an associated address, wherein the associated address points to data stored in line of memory in a lower-level hierarchical memory, wherein the line of memory has a length that is determined by the length of lines of memory stored in a higher-level hierarchical cache;
an array that includes slots for storing an indication of the address of the cache request in response to a determination that an indication of the address of the cache request is not stored within of the slots of the filter array and that is arranged to pass an indication of the stored address to a data prefetch buffer when an address window that is aligned to a power of two and is twice the length of line of memory encompasses both a stored indication of memory and an address associated with a subsequently received memory read request;
and
a prefetch filter FIFO (First In-First Out) counter that is modified to cycle through the slots of the filter array to allocate each next slot for storing subsequent indications of the address of subsequent cache requests in turn before wrapping around to a first slot of the filter array.

1 more element

Dependencies are inferred from the claim text.

Prefetch stream filter with fifo allocation and stream direction prediction

Life of this patent

Prefetch stream filter with fifo allocation and stream direction prediction

Life of this patent

Abstract

Claims20