Configurable snoop filters for cache coherent systems

Patent metadata

Field	Value
Publication number	US-2016188471-A1
Application number	US-201414588325-A
Country	US
Kind code	A1
Filing date	Dec 31, 2014
Priority date	Dec 31, 2014
Publication date	Jun 30, 2016
Grant date	—

Abstract

A cache coherent system includes a directory with more than one snoop filter, each of which stores information in a different set of snoop filter entries. Each snoop filter is associated with a subset of all caching agents within the system. Each snoop filter uses an algorithm chosen for best performance on the caching agents associated with the snoop filter. The number of snoop filter entries in each snoop filter is primarily chosen based on the caching capacity of just the caching agents associated with the snoop filter. The type of information stored in each snoop filter entry of each snoop filter is chosen to meet the desired filtering function of the specific snoop filter.

First claim

What is claimed is:

1 . A system comprising:
a set of snoop filters; a first caching agent, with a first variant of a characteristic, in communication with the set of snoop filters; a second caching agent, with a second variant of the characteristic, in communication with the set of snoop filters; a first snoop filter within the set of snoop filters arranged to store information in a first set of snoop filter entries; and a second snoop filter within the set of snoop filters arranged to store information in a second set of snoop filter entries, wherein the first caching agent is associated with the first snoop filter and the second caching agent is associated with the second snoop filter.

2 . The system of claim 1 further comprising a third caching agent, with the first variant of the characteristic, in communication with the set of snoop filters, wherein the third caching agent is associated with the first snoop filter.

3 . The system of claim 1 wherein the characteristic is presence within a coherency domain.

4 . The system of claim 1 wherein the characteristic is presence within a power domain.

5 . The system of claim 1 wherein the characteristic is a cache size.

6 . The system of claim 1 wherein the characteristic of the first caching agent is variable.

7 . The system of claim 1 wherein the first snoop filter uses a filtering algorithm and the second snoop filter does not use the filtering algorithm.

8 . The system of claim 1 wherein a type of information is stored in the first set of snoop filter entries and the type of information is not stored in the second set of snoop filter entries.

9 . The system of claim 1 wherein the number of snoop filter entries in the first set of snoop filter entries and the number of snoop filter entries in the second set of snoop filter entries are different.

10 . The system of claim 9 further comprising a multiplicity of caching agents with the first variant of the characteristic, the multiplicity of caching agents being associated with the first snoop filter, wherein the difference corresponds to the number of caching agents associated with the first snoop filter.

11 . A system-on-chip including a system, wherein the system includes:
a set of snoop filters; a first caching agent, with a first variant of a characteristic, in communication with the set of snoop filters; a second caching agent, with a second variant of the characteristic, in communication with the set of snoop filters; a first snoop filter within the set of snoop filters arranged to store information in a first set of snoop filter entries; and a second snoop filter within the set of snoop filters arranged to store information in a second set of snoop filter entries, wherein the first caching agent is associated with the first snoop filter and the second caching agent is associated with the second snoop filter.

12 . An end-user product comprising the system-on-chip of claim 11 .

13 . A cache coherent system comprising:
a first snoop filter that uses a first algorithm; and a second snoop filter that uses a second algorithm.

14 . A method of allocating snoop filter entry storage to a plurality of snoop filters in a system with a plurality of caching agents, the method comprising the steps of:
associating a first set of caching agents with a first snoop filter; associating a second set of caching agents with a second snoop filter; allocating a first number of snoop filter entries to the first snoop filter; and allocating a second number of snoop filter entries to the second snoop filter, wherein the first number of snoop filter entries and the second number of snoop filter entries are different.

15 . The method of claim 14 wherein the first number of snoop filter entries is a first integer multiple of the number of caching agents in the first set of caching agents.

16 . The method of claim 15 wherein the second number of snoop filter entries is a second integer multiple of the number of caching agents in the second set of caching agents and the first integer multiple and the second integer multiple are different.

Assignees

• Arteris Inc

Inventors

• Forrest Craig Stephen
• Kruckemyer David A

Classifications

• G06F12/0842

  for multiprocessing or multitasking · CPC title

• G06F12/0893

  Caches characterised by their organisation or structure · CPC title

• G06F2212/621

  Coherency control relating to peripheral accessing, e.g. from DMA or I/O device · CPC title

• G06F12/0871 Primary

  Allocation or management of cache space · CPC title

• G06F12/0828 Primary

  with concurrent directory accessing, i.e. handling multiple concurrent coherency transactions · CPC title