Routing for 3D Mesh Networks
Presenter: Shu YANG
Introduction
• RPM: By randomly selecting an intermediate layer,
traffic is uniformly distributed.
• Problem 1: Balanced traffic distribution does not
result in balanced thermal distribution.
• Problem 2: Bad zero-load latency.
• Problem 3: Large router area due to large crossbar.
• Problem 4: Traffic along Z direction is heavy.
Paper #1 Traffic- and Thermal-Aware Run-Time Thermal
Management Scheme for 3D NoC Systems (NOCS 2010)
• Address Problem 1
• The length of heat conduction path and power density per
unit area increase as more dies stack vertically.
• Try to decrease the temperature of overheat routers with
minimum performance impact.
– With monitoring the network status to prevent congestion, the work
loads are migrated to heat sink adaptively.
Figures taken from Chao et al "Traffic- and Thermal-Aware Run-Time Thermal Management Scheme for 3D NoC Systems"
Paper #1 (cont’d)
– The selection of downward level
depends on the traffic load
estimation of each layer.
– The actual implementation of load
estimation relies on counters,
which is updated individually
inside each router.
If (cnt3+cnt2+cnt1+cnt0 < threshold)
DW_level = 3;
else if (cnt3+cnt2+cnt1 < threshold)
DW_level = 2;
else if (cnt3+cnt2 < threshold)
DW_level = 1;
else
DW_level = 0;
Figures taken from Chao et al "Traffic- and Thermal-Aware Run-Time Thermal Management Scheme for 3D NoC Systems"
Paper #2 LA-XYZ: Low Latency, High Throughput Look-Ahead
Routing Algorithm for 3D Network-on-Chip (3D-NoC) Architecture
(MCSoC 2012)
• Address to problem 2
• Try to make XYZ routing take the best use of each pipeline
stage to decrease latency.
– look-ahead routing
– no-load bypass
Figures taken from A. Ben Ahmed, A. Ben Abdallah “LA-XYZ: Low Latency, High Throughput Look-Ahead Routing Algorithm for 3D
Network-on-Chip (3D-NoC) Architecture”
Paper #3 Partial-LastZ: An Optimized Hybridization Technique for 3D
NoC Architecture Enabling Adaptive Inter-Layer Communication
(ISOCC 2012)
• Address Problem 3
• The straightforward extension of 2D NoC structure is 3D
Symmetric NoC created by adding two physical ports to each
router; one for Up and one for Down.
• But this suffers considerably large crossbar as a result of two
extra ports.
Figures taken from R. S. Ramanujam and B. Lin “Near-optimal oblivious routing on threedimensional mesh networks”
Paper #3 (cont’d)
• Bus-based one-hop
communication
• 6*6 router is used
instead of 7*7
• LastZ-based routing
algorithm
• 5*6 router is used
instead of 6*6
Figures taken from Mingyang Zhu, Jinho Lee, Kiyoung Choi “An Adaptive Routing Algorithm for 3D Mesh NoC with Limited Vertical
Bandwidth ”
Paper #3 (cont’d)
• Partial-LastZ: enable
to support adaptivity
for inter-layer
communication by
using a mixture of
LastZ Bus and Typical
Bus
Figures taken from Mingyang Zhu, Jinho Lee, Kiyoung Choi “An Adaptive Routing Algorithm for 3D Mesh NoC with Limited Vertical
Bandwidth ”
Paper #4 An Adaptive Routing Algorithm for 3D Mesh
NoC with Limited Vertical Bandwidth (VLSI-SoC 2012)
• Address Problem 4
• Vertical links tend to have limited bandwidth when compared
to horizontal links(mainly due to reduced number of TSVs)
– High area consumption for TSV landing pads
– Relatively low yield of TSVs
• Try to distribute the traffic load locally while considering the
direction toward the destination
– Different weight is assigned to each direction
– Traffic in each direction is quantified by free buffer space
Traffic condition = free buffer space * assigned weight
Summation
• Vertical dimension is very special in 3D NoC and
should be treated separately.
• Thermal issues need to be considered carefully since
3D NoC suffers much higher power density.
Thank You