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diff --git a/docs/content/methodology/trex_traffic_generator.md b/docs/content/methodology/trex_traffic_generator.md deleted file mode 100644 index 4f62d91c47..0000000000 --- a/docs/content/methodology/trex_traffic_generator.md +++ /dev/null @@ -1,195 +0,0 @@ ---- -title: "TRex Traffic Generator" -weight: 5 ---- - -# TRex Traffic Generator - -## Usage - -[TRex traffic generator](https://trex-tgn.cisco.com) is used for majority of -CSIT performance tests. TRex is used in multiple types of performance tests, -see [Data Plane Throughtput]({{< ref "data_plane_throughput/data_plane_throughput/#Data Plane Throughtput" >}}) -for more detail. - -## Traffic modes - -TRex is primarily used in two (mutually incompatible) modes. - -### Stateless mode - -Sometimes abbreviated as STL. -A mode with high performance, which is unable to react to incoming traffic. -We use this mode whenever it is possible. -Typical test where this mode is not applicable is NAT44ED, -as DUT does not assign deterministic outside address+port combinations, -so we are unable to create traffic that does not lose packets -in out2in direction. - -Measurement results are based on simple L2 counters -(opackets, ipackets) for each traffic direction. - -### Stateful mode - -A mode capable of reacting to incoming traffic. -Contrary to the stateless mode, only UDP and TCP is supported -(carried over IPv4 or IPv6 packets). -Performance is limited, as TRex needs to do more CPU processing. -TRex suports two subtypes of stateful traffic, -CSIT uses ASTF (Advanced STateFul mode). - -This mode is suitable for NAT44ED tests, as clients send packets from inside, -and servers react to it, so they see the outside address and port to respond to. -Also, they do not send traffic before NAT44ED has created the corresponding -translation entry. - -When possible, L2 counters (opackets, ipackets) are used. -Some tests need L7 counters, which track protocol state (e.g. TCP), -but those values are less than reliable on high loads. - -## Traffic Continuity - -Generated traffic is either continuous, or limited (by number of transactions). -Both modes support both continuities in principle. - -### Continuous traffic - -Traffic is started without any data size goal. -Traffic is ended based on time duration, as hinted by search algorithm. -This is useful when DUT behavior does not depend on the traffic duration. -The default for stateless mode. - -### Limited traffic - -Traffic has defined data size goal (given as number of transactions), -duration is computed based on this goal. -Traffic is ended when the size goal is reached, -or when the computed duration is reached. -This is useful when DUT behavior depends on traffic size, -e.g. target number of NAT translation entries, each to be hit exactly once -per direction. -This is used mainly for stateful mode. - -## Traffic synchronicity - -Traffic can be generated synchronously (test waits for duration) -or asynchronously (test operates during traffic and stops traffic explicitly). - -### Synchronous traffic - -Trial measurement is driven by given (or precomputed) duration, -no activity from test driver during the traffic. -Used for most trials. - -### Asynchronous traffic - -Traffic is started, but then the test driver is free to perform -other actions, before stopping the traffic explicitly. -This is used mainly by reconf tests, but also by some trials -used for runtime telemetry. - -## Trafic profiles - -TRex supports several ways to define the traffic. -CSIT uses small Python modules based on Scapy as definitions. -Details of traffic profiles depend on modes (STL or ASTF), -but some are common for both modes. - -Search algorithms are intentionally unaware of the traffic mode used, -so CSIT defines some terms to use instead of mode-specific TRex terms. - -### Transactions - -TRex traffic profile defines a small number of behaviors, -in CSIT called transaction templates. Traffic profiles also instruct -TRex how to create a large number of transactions based on the templates. - -Continuous traffic loops over the generated transactions. -Limited traffic usually executes each transaction once -(typically as constant number of loops over source addresses, -each loop with different source ports). - -Currently, ASTF profiles define one transaction template each. -Number of packets expected per one transaction varies based on profile details, -as does the criterion for when a transaction is considered successful. - -Stateless transactions are just one packet (sent from one TG port, -successful if received on the other TG port). -Thus unidirectional stateless profiles define one transaction template, -bidirectional stateless profiles define two transaction templates. - -### TPS multiplier - -TRex aims to open transaction specified by the profile at a steady rate. -While TRex allows the transaction template to define its intended "cps" value, -CSIT does not specify it, so the default value of 1 is applied, -meaning TRex will open one transaction per second (and transaction template) -by default. But CSIT invocation uses "multiplier" (mult) argument -when starting the traffic, that multiplies the cps value, -meaning it acts as TPS (transactions per second) input. - -With a slight abuse of nomenclature, bidirectional stateless tests -set "packets per transaction" value to 2, just to keep the TPS semantics -as a unidirectional input value. - -### Duration stretching - -TRex can be IO-bound, CPU-bound, or have any other reason -why it is not able to generate the traffic at the requested TPS. -Some conditions are detected, leading to TRex failure, -for example when the bandwidth does not fit into the line capacity. -But many reasons are not detected. - -Unfortunately, TRex frequently reacts by not honoring the duration -in synchronous mode, taking longer to send the traffic, -leading to lower then requested load offered to DUT. -This usualy breaks assumptions used in search algorithms, -so it has to be avoided. - -For stateless traffic, the behavior is quite deterministic, -so the workaround is to apply a fictional TPS limit (max_rate) -to search algorithms, usually depending only on the NIC used. - -For stateful traffic the behavior is not deterministic enough, -for example the limit for TCP traffic depends on DUT packet loss. -In CSIT we decided to use logic similar to asynchronous traffic. -The traffic driver sleeps for a time, then stops the traffic explicitly. -The library that parses counters into measurement results -than usually treats unsent packets/transactions as lost/failed. - -We have added a IP4base tests for every NAT44ED test, -so that users can compare results. -If the results are very similar, it is probable TRex was the bottleneck. - -### Startup delay - -By investigating TRex behavior, it was found that TRex does not start -the traffic in ASTF mode immediately. There is a delay of zero traffic, -after which the traffic rate ramps up to the defined TPS value. - -It is possible to poll for counters during the traffic -(fist nonzero means traffic has started), -but that was found to influence the NDR results. - -Thus "sleep and stop" stategy is used, which needs a correction -to the computed duration so traffic is stopped after the intended -duration of real traffic. Luckily, it turns out this correction -is not dependend on traffic profile nor CPU used by TRex, -so a fixed constant (0.112 seconds) works well. -Unfortunately, the constant may depend on TRex version, -or execution environment (e.g. TRex in AWS). - -The result computations need a precise enough duration of the real traffic, -luckily server side of TRex has precise enough counter for that. - -It is unknown whether stateless traffic profiles also exhibit a startup delay. -Unfortunately, stateless mode does not have similarly precise duration counter, -so some results (mostly MRR) are affected by less precise duration measurement -in Python part of CSIT code. - -## Measuring Latency - -If measurement of latency is requested, two more packet streams are -created (one for each direction) with TRex flow_stats parameter set to -STLFlowLatencyStats. In that case, returned statistics will also include -min/avg/max latency values and encoded HDRHistogram data.
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