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authors: Bobby R. Bruce
last edited: 2024-04-16 17:50:15 +0000

Garnet Synthetic Traffic

The Garnet Synthetic Traffic provides a framework for simulating the Garnet network with controlled inputs. This is useful for network testing/debugging, or for network-only simulations with synthetic traffic.

Note: The garnet synthetic traffic injector only works with Garnet_standalone coherence protocol.

How to run

First build gem5 with the Garnet_standalone coherence protocol. This protocol is ISA-agnostic, and hence we build it with the NULL ISA.

For gem5 <= 23.0:

scons build/NULL/gem5.debug PROTOCOL=Garnet_standalone

For gem5 >= 23.1

scons defconfig build/NULL build_opts/NULL
scons setconfig build/NULL RUBY_PROTOCOL_GARNET_STANDALONE=y
scons build/NULL/gem5.debug

Example command:

./build/NULL/gem5.debug configs/example/garnet_synth_traffic.py  \
--num-cpus=16 \
--num-dirs=16 \
--network=garnet2.0 \
--topology=Mesh_XY \
--mesh-rows=4  \
--sim-cycles=1000 \
--synthetic=uniform_random \
--injectionrate=0.01

Parameterized Options

System Configuration       Description
--num-cpus Number of cpus. This is the number of source (injection) nodes in the network.
--num-dirs Number of directories. This is the number of destination (ejection) nodes in the network.
--network Network model: simple or garnet2.0. Use garnet2.0 for running synthetic traffic.
--topology Topology for connecting the cpus and dirs to the network routers/switches.
--mesh-rows The number of rows in the mesh. Only valid when –topology is Mesh* MeshDirCorners*



Network Configuration   Description
--router-latency Default number of pipeline stages in the garnet router. Has to be >= 1. Can be over-ridden on a per router basis in the topology file.
--link-latency Default latency of each link in the network. Has to be >= 1. Can be over-ridden on a per link basis in the topology file.
--vcs-per-vnet Number of VCs per Virtual Network.
--link-width-bits Width in bits for all links inside the garnet network. Default = 128.



Traffic Injection Configuration           Description
--sim-cycles Total number of cycles for which the simulation should run.
--synthetic The type of synthetic traffic to be injected. The following synthetic traffic patterns are currently supported: uniform_random, tornado, bit_complement, bit_reverse, bit_rotation, neighbor, shuffle, and transpose
--injectionrate Traffic Injection Rate in packets/node/cycle. It can take any decimal value between 0 and 1. The number of digits of precision after the decimal point can be controlled by --precision which is set to 3 as default in garnet_synth_traffic.py.
--single-sender-id Only inject from this sender. To send from all nodes, set to -1.
--single-dest-id Only send to this destination. To send to all destinations as specified by the synthetic traffic pattern, set to -1.
--num-packets-max Maximum number of packets to be injected by each cpu node. Default value is -1 (keep injecting till sim-cycles).
--inj-vnet Only inject in this vnet (0, 1 or 2). 0 and 1 are 1-flit, 2 is 5-flit. Set to -1 to inject randomly in all vnets.



Implementation of Garnet Synthetic Traffic

The synthetic traffic injector is implemente in GarnetSnytheticTraffic.cc. The sequence of steps involved in generating and sending a packet are as follows.