System with virtual address networks and split ownership and access right coherence mechanism

A computer system comprising:

• a plurality of active devices, wherein each active device includes a cache, wherein the plurality of active devices includes a first active device that includes a first cache;
• a directory configured to indicate which of the plurality of active devices has an ownership responsibility for a given coherency unit;
• an address network configured to convey address packets between the plurality of active devices and the directory, wherein the address network includes a response virtual network configured to convey response packets and a broadcast virtual network configured to convey invalidating packets;
• a data network configured to convey data packets between the plurality of active devices;
• wherein the directory is configured to send a response packet to the first active device on the response virtual network and to send invalidating packets to the plurality of active devices on the broadcast virtual network;
• wherein the first active device is configured to transition an ownership responsibility for a first coherency unit cached in the first cache upon receipt of the response packet and to transition an access right to the first coherency unit cached in the first cache upon receipt of a corresponding data packet, wherein the ownership responsibility transitions at a different time than the access right transitions.

A method of maintaining cache coherency in a computer system, the method comprising:

• a first active device sending a first address packet requesting an access right to a first coherency unit, wherein the first active device includes a first cache;
• in response to said first active device sending, a directory sending a response address packet on a response virtual network to the first active device and sending invalidating address packets to one or more active devices on a multicast virtual network;
• the first active device transitioning an ownership responsibility for the first coherency unit cached in the first cache upon receiving the response address packet from the directory and gaining the access right to the first coherency unit cached in the first cache upon receiving a corresponding data packet;
• wherein said transitioning the ownership responsibility occurs at a different time than said transitioning the access right.

A method of maintaining cache coherency in a computer system, the method comprising:

• a first active device initiating a coherence transaction to gain an access right to a first coherency unit;
• in response to said initiating, a response virtual address network conveying a first address packet to the first active device;
• in response to said initiating, a multicast virtual address network conveying a second address packet to the first active device and to a second active device;
• the first active device receiving a data packet corresponding to the first coherency unit;
• in response to receiving the second address packet and the data packet, the first active device gaining the access right to the first coherency unit.

A computer system comprising:

• a plurality of active devices, wherein each active device includes a cache, wherein the plurality of active devices includes a first active device that includes a first cache;
• a directory configured to indicate which of the plurality of active devices has an ownership responsibility for a given coherency unit;
• an address network configured to convey address packets between the plurality of active devices and the directory, wherein the address network includes a response virtual network configured to convey response packets and a broadcast virtual network configured to convey invalidating packets;
• a data network configured to convey data packets between the plurality of active devices;
• wherein the directory is configured to send a response packet to the first active device on the response virtual network and to send invalidating packets to the plurality of active devices on the broadcast virtual network;
• wherein the first active device is configured to transition its access right to the first coherency unit in response to sending a data packet corresponding to the first coherency unit on the data network.

A computer system comprising:

• a plurality of means for accessing data, wherein each means for accessing data includes a cache for storing data accessed by that means for accessing data, wherein the plurality of means for accessing data includes a first means for accessing data, wherein the first means for accessing data includes a first cache;
• means for storing ownership information associated with one or more coherency units;
• means for conveying coherence requests between the plurality of means for accessing data and the means for storing ownership information, wherein the means for conveying coherence requests includes virtual means for conveying responses and virtual means for conveying invalidating requests;
• means for conveying data between the plurality of means for accessing data;
• wherein the means for storing ownership information conveys one or more invalidating requests to one or more of the means for processing data and conveys a response to the first means for processing data;
• wherein the first means transitions an ownership responsibility for the first coherency unit cached in the first cache upon receiving the response coherence request;
• wherein the first means transitions an access right to the first coherency unit cached in the first cache upon receiving corresponding data on the means for conveying data;
• wherein the access right transitions at a different time than the ownership responsibility transitions.