Cache allocation based on quality-of-service monitoring

A method of operating a cache to provide data caching in response to data access requests from at least one system device comprising:

• caching data items returned from memory in response to the data access requests in data caching storage having multiple entries;
• in response to absence of a requested data item in the data caching storage, allocating an entry of the multiple entries in the data caching storage in dependence on a cache allocation policy;
• modifying the cache allocation policy with respect to allocation of the entry for the requested data item in response to a quality-of-service indication;
• and
• holding at least one data transaction pending transmittal in a shared memory transaction queue to that holds pending memory transactions for multiple system devices, where the quality-of-service indication is a status indication that signifies allocating an entry of the multiple entries in the data caching storage circuitry for caching the requested data item according to the cache allocation policy, and evicting a data item from the cache into the shared memory transaction queue, would cause a number of entries in the shared memory transaction queue for to be available to a given system device to fall below a threshold minimum.

A cache to provide data caching in response to data access requests from at least one system device comprising:

• means for caching data items returned from memory in response to the data access requests in data caching storage having multiple entries;
• means for allocating an entry of the multiple entries in the data caching storage in dependence on a cache allocation policy in response to absence of the requested data item in the data caching storage;
• means for modifying the cache allocation policy with respect to allocation of the entry for the requested data item in response to a quality-of-service indication;
• and
• means to hold at least one data transaction pending transmittal to memory in a shared memory transaction queue for multiple system devices,
• where the quality-of-service indication is a status indication received from the transaction queue circuitry,
• the status indication signifying that allocating an entry of the multiple entries in the data caching storage circuitry for caching the requested data item according to the cache allocation policy, and evicting a data item stored in the cache into the shared memory transaction queue, would cause a number of entries in the shared memory transaction queue to be available to a given system device to fall below a threshold minimum.