Cache consistency in a multiprocessor system with shared memory
View Patent ↗A process to make the cache memory of a processor consistent includes the processor processing a request to write data to an address in its memory marked as being in the shared state. The address is transmitted to the other processors, data are written into the processor's cache memory and the address changes to the modified state. An appended memory associated with the processor memorizes the address, the data and an associated marker in a first state. The processor then receives the address with an indicator. If the indicator indicates that the processor must perform the operation and if the associated marker is in the first state, the data are kept in the modified state. If the indicator does not indicate that the processor must perform the operation and if the processor receives an order to mark the data to be in the invalid state, the marker changes to a second state.
1. A MESI protocol state process, comprising:
a modified state;
an exclusive state;
a shared state;
an invalid state; and
an intermediate state between the shared state and the modified state, wherein the intermediate state is entered into when a first processor processes a request to write certain data to an address in its cache memory marked as being in the modified state, and
wherein if the first processor subsequently receives a request to perform a memory operation on the certain data then the modified state is entered into in the first processor, and the invalid state is entered into for other processors, or
wherein if the first processor subsequently receives an indication that the other processor is operating on the certain data then the invalid state is entered into in the first processor.
2. The process of claim 1 wherein, when in the intermediate state between the shared state and the modified state by the first processor, the other processor remains in the shared state with respect to that certain data.