An arbiter decides to grant access from multiple clients to a shared resource (e.g. memory) using efficiency and/or urgency terms. Urgency for a client may be determined based on an "in-band" request identifier transmitted from the client to the resource along with the request, and an "out-of-band" request identifier that is buffered by the client. A difference between the out-of-band request identifier and the in-band request identifier indicates the location of the request in the client buffer. A small difference indicates that the request is near the end of the buffer (high urgency), and a large difference indicates that the request is far back in the buffer (low urgency). Efficiency terms include metrics on resource overhead, such as time needed to switch between reading/writing data from/to memory via a shared memory bus, or bank management overhead such as time for switching between DRAM banks.