On-chip Networks for Manycore Architecture Myong ... - People - MIT

5
Shuffle (Burst)
6
Uniform Random (Burst)
4.5
5.5
Total Throughput (packets/cycle)
4
3.5
3
2.5
2
1.5
U=2,B=0
U=1,B=2,N=1
U=1,B=2,N=10
U=1,B=2,N=16
U=1,B=2,N=25
U=1,B=2,N=100
1
0 10 20 30 40 50 60 70
Offered Injection Rate (packets/cycle)
Total Throughput (packets/cycle)
5
4.5
4
3.5
3
2.5
2
1.5
U=2,B=0
U=1,B=2,N=1
U=1,B=2,N=10
U=1,B=2,N=16
U=1,B=2,N=25
U=1,B=2,N=100
1
0 10 20 30 40 50 60 70
Offered Injection Rate (packets/cycle)
Figure 3-11: BAN performance under bursty tra
periods (N)
c with various link arbitration
1
(thereby lessening the impact of a dead cycle to ) and limiting the network’s
N+1
adaptivity to rapid changes in tra
the relevant tradeo↵s.
c patterns. The results in this section illustrate
Figure 3-10 shows how often each bidirectional link actually changes its direction
under bursty shu✏e and uniform-random tra
c: the x-axis shows how frequently
links’ directions change and the y-axis shows how many links switch that often. For
example, under shu✏e tra
c, only 8% of the bidirectional links change their direction
more frequently than once in two hundred cycles. Tra c exhibiting the uniformrandom
pattern, in comparison, is more symmetric than shu✏e, and so the link
directions change more often.
The observation that no link changes its direction more frequently than once in
ten cycles led us to investigate how infrequent the link switches could be without
significantly a↵ecting performance. In Figure 3-11 we compare the performance of
the bidirectional network under di↵erent link arbitration frequencies; as expected,
throughput decreases when the links are allowed to switch less often.
Even with a switching period as large as 100 cycles, the bidirectional network still
significantly outperforms the unidirectional design under many loads (e.g., by more
than 20% for shu✏e). In the case of uniform-random, however, the bidirectional network
performance trails the unidirectional design when switching is infrequent. This
is because, when each link arbitration decision lasts 100 cycles, any temporary benefit
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