PCI Express System Architecture

Modified Ordering Rules Improve Performance

This section describes how temporary transaction blocking can occur when the strong ordering rules listed in Table 8-2 are rigorously enforced. Modification of strong ordering between transactions that do not violate the Produce/Consumer programming model can eliminate many blocking conditions and improve link efficiency.

Strong Ordering Can Result in Transaction Blocking

Maintaining the strong ordering relationship between transactions would likely result in instances where all transactions would be blocked due to a single receive buffer being full. The strong ordering requirements to support the Producer/Consumer model cannot be modified (except in the case of relaxed ordering described previously). ...