Computer system and control method thereof

A control method enabling a storage system comprising a first controller and a second controller coupled to each other, wherein the first controller includes a first processor and a first shared memory, and the second processor includes a second processor and a second shared memory;

• and wherein data stored in the first shared memory and the second shared memory is to be used by the first processor and the second processor, comprising:
• receiving, by the first controller, an I/O request from a host coupled to the storage system;
• transmitting, by the first controller, request information which is to be processed by the second processor according to the I/O request;
• wherein, when the request information requests the second processor to access the second shared memory, the request information is transmitted as first request information indicating its priority to the second processor, and the first controller waits for a response from the second processor before processing the next process;
• wherein, when the request information requests the second processor to transfer data, the request information is transmitted as second request information which requests data transmission to the second processor without priority indication, and the first controller processes the next process without waiting for a response from the second processor;
• further the control method comprising:
• prioritizing, by the second controller, a processing of the first request information over other processes;
• not prioritizing, by the second controller, a processing of the second request information over other processes;
• and
• sending back, by the second controller, the response to the first processor.