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layout: documentation title: “Garnet Synthetic Traffic” doc: gem5 documentation parent: ruby permalink: /documentation/general_docs/ruby/garnet_synthetic_traffic/ author: Jason Lowe-Power

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.

Related files

• 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.

scons build/NULL/gem5.debug PROTOCOL=Garnet_standalone

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. 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.