Parallel Computer Architecture

7.1 Scalability 461

P/

64

(128) = É.Ïìâ + ß }?*

B

+0.200ì3^÷6 = 14.2 ì5 at 64 nodes and

Ñ/

Éé024

(128) = 1.0 ì5 + ß ^

Â

+ 0.200 ì5^ ÷ 10 = 23 μâ at 1,024 nodes. ■

In practice, an important connection exists between bandwidth and latency that

is overlooked in Example 7.1. If two transfers involve the same node or utilize the

same wires within the network, one may delay the other due to contention for the

shared resource. As more of the available bandwidth is utilized, the probability of

contention increases and the expected latency increases. In addition, queues may

build up within the network, further increasing the expected latency. This basic sat ...