Keeping P4 Switches Fast and Fault-free through Automatic Verification

Abstract

The networking dataplane is going through a paradigm shift as softwarization of switches sees an increased pull from the market. Yet, software tooling to support development with these new technologies is still in its infancy.In this work, we introduce a framework for verifying performance requirement conformance of data plane protocols defined in the P4 language . We present a framework that transforms a P4 program in a versatile symbolic formula which can be utilized to answer various performance queries. We represented the system using denotational semantics and it can be easily extended with low-level target-dependent information. We demonstrate the operation of this system on a toy specification.

Control flow based cost analysis for P4

“…We now evaluate the cost formula with specific parameters and inspect how parameters change program behavior. Using the data (partly utilized also in our earlier work [2]) in Table 2 to instantiate the formula in Equation 6, we obtained the graph in Figure 3. This plot exemplifies how increasing the cache size from 128B to 1024B results in decreasing execution costs.…”

“…In our earlier approach to P4 cost analysis [2], we syntactically transformed the code of P4 parsers into cost expressions. In the current paper, we utilized our earlier insights and continued this analysis with deparsing and lookup tables, but our current algorithm is based on CFG traversal.…”

“…Deparsing is the final step of the packet processing pipeline, the "inverse" operation of parsing (which we already discussed in [2]). In DeparseImpl in Listings 1, we select the headers to be included in the outgoing packet.…”

“…It is important to note that compilers may generate code that diverges from this model. Here, we assumed that the packet headers are extracted into temporary stores in Headers during parsing (as is done by our model in [2], and also by the P4 reference switch [6]). As such, in the deparsing stage we only had to move around pointers without copying larger data (except in the last line).…”

“…Using the pseudocode, we can now easily generate a cost formula per Equation 1, characterizing the average execution cost of function deparse. Using the data in Table 2 of Section 5.2 (partly utilized also in our earlier work [2]), we map the statements to elementary instructions whose costs are known, and sum up the results. As the control flow is linear, there is only one path and it is sure to be executed.…”