Snoop filter with disaggregated vector table

A method, comprising:

• receiving a request from an agent to access a coherence granule (cogran) and to allocate an agent ID to one of a plurality of snoop filter (SFT) entries in an SFT;
• performing a tag lookup function for a tag of the cogran in the SFT to find a matched SFT entry, wherein the matched SFT entry is tracking the tag of the cogran;
• determining that the number n of agents being tracked by the matched SFT entry is above a threshold;
• determining that a disaggregated vector table (DVT) entry is available;
• setting the matched SFT entry's tracking_mode to DVT;
• and
• storing a DVT index in the tracking_info field of the matched SFT entry, wherein the DVT index selects a DVT entry in a DVT, and wherein the selected DVT entry holds a tracking vector to track the agents that have cached the cogran for the matched SFT entry.

One or more physically manufactured computer-readable storage media, encoding computer-executable instructions for executing on a computer system a computer process, comprising:

• receiving a request from an agent to access a coherence granule (cogran) and to allocate an agent ID to one of a plurality of snoop filter (SFT) entries in an SFT;
• performing a tag lookup function for a tag of the cogran in the SFT to find a matched SFT entry, wherein the matched SFT entry is tracking the tag of the cogran;
• determining that the number n of agents being tracked by the matched entry is above a threshold;
• storing a DVT index in the tracking_info field of the matched SFT entry, wherein the DVT index selects a DVT entry in a disaggregated vector table (DVT), wherein the selected DVT entry is configured to hold a tracking vector for tracking the agents that have cached the cogran for the matched SFT entry;
• calculating an error correction code (ECC) of a DVT entry;
• determining that the calculated ECC does not match a value of a protection field of the DVT entry;
• and
• changing a value of the tracking_mode field of the matched SFT entry to IMPRECISE.

A system comprising:

• memory;
• a processor unit;
• and
• a cache coherence system stored in the memory that executes computer process comprising:
• receiving a request from an agent to access a coherence granule (cogran) and to allocate an agent ID to one of a plurality of snoop filter (SFT) entries in an SFT;
• performing a tag lookup function for a tag of the cogran in the SFT to find a matched SFT entry, wherein the matched SFT entry is tracking the tag of the cogran;
• determining that the number n of agents being tracked by the matched SFT entry is above a threshold, and storing a disaggregated vector table (DVT) index in the tracking_info field of the matched SFT entry, wherein the DVT index selects a DVT entry in a DVT, and wherein the selected DVT entry holds a tracking vector to track the agents that have cached the cogran for the matched SFT entry;
• determining that an agent needs to be removed from an SFT entry;
• in response to determining that an agent needs to be removed from an SFT entry, determining if the SFT entry's tracking_mode is DVT;
• and
• in response to determining that the SFT entry's tracking_mode is DVT:
• reading a precise tracking vector from a DVT entry associated with the SFT entry, and
• clearing the read DVT entry's tracking vector bit position corresponding to the agent being removed from the SFT entry.