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TLM - Modelling Contention

When more than one client wants to use a resource at once we have contention.

Real queues are used in hardware, either in FIFO memories or by flow control applying back pressure on the source to stall it until the contended resource is available. An arbiter allocates a resource to one client at a time.

Contention can be modelled using real or virtual queues:

  1. In a low-level model, the real queues are modelled in detail.
  2. A TLM model may queue the transactions, thereby blocking the client's thread until the transaction can be served.
  3. Alternatively, the transactions can be run straightaway and an estimated delay can be added to the client's delay account.

Delay estimates can be based on dynamic measurements of utilisation at the contention point, in terms of transactions per millisecond and a suitable formula, such as 1/(1-p) that models the queuing delay in terms of the utilisation.

(C) 2008-10, DJ Greaves, University of Cambridge, Computer Laboratory.