Miguel Gorgues, Dong Xiang, Jose Flich, Zhigang Yu and Jose Duato Uni. Politecnica de Valencia, Spain School of Software, Tsinghua University, China, Achieving.
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Slide 1
Miguel Gorgues, Dong Xiang, Jose Flich, Zhigang Yu and Jose
Duato Uni. Politecnica de Valencia, Spain School of Software,
Tsinghua University, China, Achieving Balanced Buffer Utilization
with a Proper Co-Design of Flow Control and Routing Algorithm
1
Slide 2
Index 1. Introduction 2. Flow control techniques and routing
algorithm 1. Overview TBFC+SUR 2. TBFC 3. SUR 4. TBFC+SUR results
3. Conclusions 2
Slide 3
Index 1. Introduction 2. Flow control techniques and routing
algorithm 1. Overview TBFC+SUR 2. TBFC 3. SUR 4. TBFC+SUR results
3. Conclusions 3
Slide 4
Introduction Current CMP systems are constructed by replicating
tiles Tiles are made of: router, processor and hierarchy cache
memory Networks on chip (NOC) are responsible for communicating
these tiles The performance of the NoCs depend on: routing,
congestion, traffic, topology Tilera (64 cores) 4
Slide 5
Introduction What is routing? Routing types: Routing tables
Memory tables !! Routing based on logic XY, Full Adaptive,
Odd-even... What does the adaptive routing provide? Improved
utilization of network resources Alternative paths to route the
messages Better network performance Requirements: Virtual channel
(VC) differentiation, adaptive or escape channel 5
Slide 6
Introduction However some problems arise when using FA
Unbalanced utilization of the network resources Our proposals to
solve this problem are: Type-Based-Flow Control (TBFC): flow
control mechanism based on types Safe-Unsafe Routing (SUR): routing
algorithm that labels the messages with the type Fully adaptive 6
However some problems arise when using FA Unbalanced utilization of
the network resources Our proposals to solve this problem are:
Type-Based-Flow Control (TBFC): flow control mechanism based on
types Safe-Unsafe Routing (SUR): routing algorithm that labels the
messages with the type Fully adaptive TBFC+SUR
Slide 7
Index 1. Introduction 2. Flow control techniques and routing
algorithm 1. Overview TBFC+SUR 2. TBFC 3. SUR 4. TBFC+SUR results
3. Conclusions 7
Slide 8
Context 8 Assume the Virtual Cut-through is used Packet size is
equal to buffer size Packet- Level Crossbar Switching
Slide 9
Overview TBFC+SUR Goal : achieve a proper balanced utilization
of input port buffers. Classification of messages in different
types Message type depend on the routing Flow control according to
the number of messages of each type in the downstream switch
Message type 0 Message type 1 9
Slide 10
TBFC(I) Router based on Credits flow control Router is made up
with four stages: IB, RT, VA/SA, X Both arbiters VA and SA control
the crossbar access Messages can be forwarded if there are enough
credits 10
Slide 11
TBFC(II) Router TBFC with Packet-Level Crossbar Switching
Reduce required control Info Reduce network traffic IB Filter only
for deterministic routings 11
Slide 12
TBFC(III) 12 TYPE is the number of green messages in the next
input port
Slide 13
SUR(I) SAFE-UNSAFE Routing SUR is fully adaptive routing and
relies on an escape path to prevent deadlock The underline routing
algorithm to implement the escape path is Dimension Order Routing
(DOR) SUR labels the packets as safe or unsafe Allows routing in
mesh and torus Each input port contains two VCs, while each VC is
assigned a buffer to keep the whole packet. Use Virtual Cut-Through
Allows to use Flit-Level and Packet-Level Crossbar Switching
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Slide 14
SUR(II) The SUR algorithm along with TBFC ensure that safe type
messages always have reserved one virtual channel at the input
port: A virtual channel contains a message labeled as safe There is
an empty virtual channel that can store a packet of type safe
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Slide 15
SUR(III) 15 Packets are labeled when they are sent to a
downstream router as follows: In an n-dimensional mesh a packet is
delivered and kept in the next router as a safe packet if the next
hop conforms to the baseline routing algorithm(DOR). In an
n-dimensional torus a packet is delivered and labeled in the next
router as safe if one of the following conditions is met: The next
hop of the packet is to traverse a wraparound link along dimension
d, and the packet does not need to traverse a wraparound link with
a lower dimension than d. The packet does not need to traverse any
wraparound link from the current router to the destination and the
next hop conforms to the baseline routing. If any of these two
conditions is not met, then, the packet is delivered and labeled as
unsafe packet.
Slide 16 1 FREE = 1 & TYPE > 0 FREE = 1 & TYPE = 0
and the message will be labeled as safe 16">
SUR(IV) Being the flow control parameters, "FREE", the number
of free VCs and "TYPE", the number of messages labeled as safe in
the downstream input port. SUR allows to forward a message when one
of these conditions are met FREE > 1 FREE = 1 & TYPE > 0
FREE = 1 & TYPE = 0 and the message will be labeled as safe
16
Slide 17
SUR(V) Deadlock-freedom property Let us assume a 2D mesh Safe
messages in green Unsafe messages in red Deadlock: all the buffers
are full in the cycle the routing restrictions do not allow packets
to advance 17
Slide 18
SUR(VI) Deadlock-freedom property Deadlock: all the buffers are
full in the cycle Cannot be produced because the Y X dependence
produces messages labeled as unsafe SUR rules dont allow to fill
all the virtual channels of the same input port only with messages
labeled as unsafe 18
Slide 19
SUR(VII) Deadlock-freedom property Deadlock: the routing
restrictions do not allow packets to advance At least one VC has to
contain one safe packet or has to be free to store one Therefore,
it is always possible to transmit this packet type and ensuring
deadlock free paths 19
Slide 20
SUR(VII) 20 Safe messages colored in green Unsafe messages
colored in red
TBFC+SUR results (II) Performance evaluation for transpose
traffic in 8 8 mesh networks. Performance evaluation for uniform
traffic in 8 8 mesh networks. 22
Slide 23
TBFC+SUR results (III) RoutingVCsQueue size XY220 flits FA320
flits FA_Bubble220 flits adap, 40 flits escape SUR_2VC220 flits
SUR_3VC320 flits Parameters for simulations in 2D torus Same
parameters as 2D mesh Some modifications in VCs and queue size for
routing needs
Slide 24
TBFC+SUR results (IV) Performance evaluation for uniform
traffic in 8 8 torus networks. Performance evaluation for transpose
traffic in 8 8 torus networks.
Slide 25
TBFC+SUR results(V) VCs balanced utilization 25
Slide 26
Index 1. Introduction 2. Flow control techniques and routing
algorithm 1. Overview TBFC+SUR 2. TBFC 3. SUR 4. TBFC+SUR results
3. Conclusions 26
Slide 27
Conclusions This paper presents a novel flow control Type-Based
Flow- Control (TBFC) with Safe/Unsafe routing algorithm (SUR) which
allows an optimized balanced buffer utilization. The combination of
TBFC and SUR allows us to reduce the number of VCs required to
implement fully adaptive routing algorithms in tori. The results
showed that the proposed TBFC with SUR algorithm outperform better
than the previous methods under different communication patterns.
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Slide 28
Achieving Balanced Buffer Utilization with a Proper Co-Design
of Flow Control and Routing Algorithm 28