authors: Jason Lowe-Power
last edited: 2024-06-01 14:26:34 +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 the Garnet_standalone coherence protocol.

How to run

First build gem5 with the Garnet_standalone coherence protocol. The Garnet_standalone 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 build/NULL/gem5.debug

Example command:

./build/NULL/gem5.debug configs/example/  \
        --num-cpus=16 \
        --num-dirs=16 \
        --network=garnet \
        --topology=Mesh_XY \
        --mesh-rows=4  \
        --sim-cycles=1000 \
        --synthetic=uniform_random \

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 garnet. Use garnet for running synthetic traffic.
–topology Topology for connecting the cpus and dirs to the network routers/switches. More detail about different topologies can be found (here)[Interconnection_Network#Topology].
–mesh-rows The number of rows in the mesh. Only valid when ‘’–topology’’ is ‘‘Mesh_’’ or ‘‘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 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 ‘‘’’.
–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 implemented in The sequence of steps involved in generating and sending a packet are as follows.