US 2018/0004663 A1Published application

Progressive fine to coarse grain snoop filter

AssigneeArm Limited

InventorsJamshed JALAL, Mark David WERKHEISER

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Abstract

A data processing system includes a snoop filter organized as a number of lines, each storing an address tag associated with the address of data stored in one or more caches of the system, a coherency state of the data, and presence data. A snoop controller sends snoop messages in response to data access requests. The presence data is configurable in a first format, in which the value of a bit in the presence data is indicative of a subset of the nodes for which at least one node in the subset has a copy of the data in its local cache, and in a second format, in which the presence data comprises a unique identifier of a node having a copy of the data in its local cache. The snoop controller sends snoop messages to the nodes indicated by the presence data.

Claims15

Dependent claims

A method of operation of a snoop filter of a data processing system having a plurality of nodes, where each request node has a local cache, where the plurality of nodes are grouped in a plurality of subsets and where each subset consists of one or more nodes, the method comprising:

accessing the snoop filter, dependent upon a data address received from a first node of the plurality of nodes, to retrieve format data and presence data, where the format data is indicative of a format of the presence data;
when the format data indicates a first format for the presence data:
determining, from the retrieved presence data, one or more unique identifiers of nodes from the retrieved presence data, each of the one or more identified nodes having a copy of data associated with the data address in its local cache;
and
sending a snoop message to each of the one or more nodes;
and
when the format data indicates a second format for the presence data:
identifying, from positions of set bits within the retrieved presence data, one or more subsets of the plurality of subsets;
and
sending a snoop message to each node in each of subset of the identified one or more subsets.

7 more elements

A data processing apparatus comprising:

a plurality of nodes, each having a local cache in which data associated with a data address may be stored;
a snoop filter organized as a plurality lines, each line comprising:
an address tag field configured to store an address tag associated with the data address;
a status field configured to store a coherency state of data stored in one or more local caches of the nodes;
and
a presence field configured to store presence data;
a snoop controller operable to receive data access requests from one or more of the plurality of nodes and further operable to send snoop messages to one or more of the plurality of nodes;
where the presence field is configurable in a first format in which the presence data comprises a unique identifier of a node, the unique identifier indicating a node having a copy in its local cache of the data associated with the data address,
where the presence field is configurable in a second format in which the value of a bit in the presence data is indicative of whether the data associated with the data address is stored in at least one local cache of a subset of nodes associated with the bit,
and
where the snoop controller is configured to send snoop messages to one or more nodes indicated by the presence data stored in the presence field of the snoop filter.

8 more elements

Dependencies are inferred from the claim text.

Facts

Application: 15/196,266Filed 29 Jun 2016
Published: 4 Jan 2018
Term ends: Not estimatedThe source records don’t support an estimate.

Classification8 codes

G06F 12/0831
Cache consistency protocols: using a bus scheme, e.g. with bus monitoring or watching means
G06F 12/0811
Multiuser, multiprocessor or multiprocessing cache systems: with multilevel cache hierarchies
G06F 12/0833
Using a bus scheme, e.g. with bus monitoring or watching means: in combination with broadcast means
G06F 12/084
Multiuser, multiprocessor or multiprocessing cache systems: with a shared cache