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.

configs/example/garnet_synth_traffic.py: file to invoke the network tester
src/cpu/testers/garnet_synthetic_traffic: files implementing the tester.
- GarnetSyntheticTraffic.py
- GarnetSyntheticTraffic.hh
- GarnetSyntheticTraffic.cc

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 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=garnet \
        --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 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 ‘‘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 implemented in GarnetSyntheticTraffic.cc. The sequence of steps involved in generating and sending a packet are as follows.

Every cycle, each cpu performs a bernouli trial with probability equal to –injectionrate to determine whether to generate a packet or not.
If –num-packets-max is non negative, each cpu stops generating new packets after generating –num-packets-max number of packets. The injector terminates after –sim-cycles.
If the cpu has to generate a new packet, it computes the destination for the new packet based on the synthetic traffic type (–synthetic).
This destination is embedded into the bits after block offset in the packet address.
The generated packet is randomly tagged as a ReadReq, or an INST_FETCH, or a WriteReq, and sent to the Ruby Port (src/mem/ruby/system/RubyPort.hh/cc).
The Ruby Port converts the packet into a RubyRequestType:LD, RubyRequestType:IFETCH, and RubyRequestType:ST, respectively, and sends it to the Sequencer, which in turn sends it to the Garnet_standalone cache controller.
The cache controller extracts the destination directory from the packet address.
The cache controller injects the LD, IFETCH and ST into virtual networks 0, 1 and 2 respectively.
- LD and IFETCH are injected as control packets (8 bytes), while ST is injected as a data packet (72 bytes).
The packet traverses the network and reaches the directory.
The directory controller simply drops it.

Garnet Synthetic Traffic

Related files

How to run

Parameterized Options

Implementation of Garnet synthetic traffic