Bus overload

The bus can become a bottleneck too, depending on relative CPU, network and bus speed.

Very similar to congestion on a network:

demand exceeds capacity;

clients queue up for transactions (in the arbiter);

no "packet loss", but operations might be terribly slow.

Simple example: single PCI bus, quad-ethernet driven at full rate. Reading register from a card:

status = CSR_READ_4(sc, DC_ISR) ;

~200ns in idle conditions
measured up to 25us under load (no typo, 100 times slower)