Sharad Chole, Andrew Fingerhut, Sha Ma, Anirudh Sivaraman, Shay Vargaftik, Alon Berger, Gal Mendelson, Mohammad Alizadeh,
Shang-Tse Chuang, Isaac Keslassy, Ariel Orda and Tom Edsall,
"dRMT: Disagreggated Programmable Switching,"
ACM SIGCOMM, Los Angeles, CA, August 2017.
[Also presented at P4 workshop 2017: slides.]
We present dRMT (disaggregated Reconfigurable Match-Action
Table), a new architecture for programmable switches. dRMT overcomes
two important restrictions of RMT, the predominant pipelinebased
architecture for programmable switches: (1) table memory
is local to an RMT pipeline stage, implying that memory not used
by one stage cannot be reclaimed by another, and (2) RMT is hardwired
to always sequentially execute matches followed by actions
as packets traverse pipeline stages. We show that these restrictions
make it difficult to execute programs efficiently on RMT.
dRMT resolves both issues by disaggregating the memory and compute resources of a programmable switch. Specifically, dRMT moves table memories out of pipeline stages and into a centralized pool that is accessible through a crossbar. In addition, dRMT replaces RMTís pipeline stages with a cluster of processors that can execute match and action operations in any order.
We show how to schedule a P4 program on dRMT at compile time to guarantee deterministic throughput and latency. We also present a hardware design for dRMT and analyze its feasibility and chip area. Our results show that dRMT can run programs at line rate with fewer processors compared to RMT, and avoids performance cliffs when there are not enough processors to run a program at line rate. dRMTís hardware design incurs a modest increase in chip area relative to RMT, mainly due to the crossbar.
The GitHub repository of the dRMT project contains all the paper-related scripts.
Extended version of the paper with:.