Our new Journal extension of Metron “High Performance NFV Service Chaining Even in the Presence of Blackboxes”

Georgios P. Katsika, Tom Barbette, Dejan Kostić, JR. Gerald Q. Maguire, Rebecca Steinert

The NSDI version of Metron supported the integration of blackbox network functions (NFs) using ring buffers. This choice limited Metron’s applicability, as real networks might contain hardware blackboxes (also known as middleboxes) or closed-source blackbox binaries running inside virtual machines (VMs) or containers. In this extended journal version published in ACM Transaction on Computer Systems, we put special effort on integrating these important blackbox types into Metron, while maintaining Metron’s hardware-level performance.

Metron achieves 100G for a chain of VNF, up to 8* better efficiency than SoTA. Check the paper for more details.

This integration was not trivial as it involved tedious low-level system aspects related to (i) efficiently dispatching packets without introducing unnecessary inter-core communication and (ii) techniques to allow high-speed service chaining. These were key principles of Metron that we wanted to maintain. Moreover, we incorporated the latest functionalities of modern 100 GbE NICs, such as single root I/O virtualization (SR-IOV) that enables physical to virtual NIC dispatching, avoiding the need for software switching. Metron instructs the physical NIC to tag the packets according to the core associated with a traffic class by the controller. The tag can then be used to dispatch packets to queues just as a Metron agent does.

As appeared in USENIX NSDI 2018, the original Metron system demonstrated an experiment on dynamic scaling at 10 Gbps. 100 GbE deployments are becoming the new commodity. Therefore, we put substantial effort on refining Metron’s scaling algorithm. Part of this algorithm uses our new method for deriving the load of a CPU core even when this core performs NIC polling (e.g., using DPDK poll mode drivers).

Metron rapidly reacts to change in the input load, see Fig 16 for more details

The 100 GbE testbed used in the NSDI version of Metron exhibited hardware limitations that prevented Metron from reaching line-rate performance. In this journal, we repeated the same experiment on two additional testbeds: First we upgraded the 100 GbE NICs of the original testbed (i.e., replacing the Mellanox ConnectX-4 with newer Mellanox ConnectX-5 NICs) and managed to increase the maximum throughput at 85 Gbps (76 Gbps was the previous limit). Then, we also upgraded the servers of the testbed using new workstations with Intel’s Skylake hardware architecture (the old servers used Intel’s Haswell hardware architecture) and managed to achieve line-rate 100 Gbps packet processing.

The paper also presents a dozen other novelties compared to the NSDI version, so check it out!

Paper (open access)

High-speed Connection Tracking in Modern Servers

Our paper “High-speed Connection Tracking in Modern Servers” will be presented by Massimo Girondi at the IEEE HPSR 2021, the 22nd International Conference on High-Performance Switching and Routing.

We have analyzed the performances of six different Hash Tables implementations, studying how to scale them across multiple cores and how to efficiently remove expired entries, benchmarking them with up to 100 Gbps traffic.

This is joint work Marco Chiesa and Massimo Girondi, the first author.

Read the paper here.

Our upcoming paper at PAM : “NICBench”

We’re pleased to announce our upcoming paper “What you need to know about (Smart) Network Interface Cards” by G. Katsikas, T. Barbette, M. Chiesa, D. Kostic and G. Maguire Jr. is accepted at PAM’21!

We can’t publish the preprint yet, but we’ll do as soon as possible 🙂

Network interface cards (NICs) are fundamental components of modern high-speed networked systems, supporting multi-100 Gbps speeds and increasing programmability. Offloading computation from a server’s CPU to a NIC frees a substantial amount of the server’s CPU resources, making NICs key to offer competitive cloud services. Therefore, understanding the performance benefits and limitations of offloading a networking application to a NIC is of paramount importance. In this paper, we measure the performance of four different NICs from one of the largest NIC vendors worldwide, supporting 100 Gbps and 200 Gbps. We show that while today’s NICs can easily support multi-hundred-gigabit throughputs, performing frequent update operations of a NIC’s packet classifier — as network address translators (NATs) and load balancers would do for each incoming connection — results in a dramatic throughput reduction of up to 70 Gbps or complete denial of service. Our conclusion is that all tested NICs cannot support high-speed networking applications that require keeping track of a large number of frequently arriving incoming connections. Furthermore, we show a variety of counter-intuitive performance artefacts including the performance impact of using multiple tables to classify flows of packets.

PAM will be held in late March, so stay tuned!

FOSDEM’21: FastClick and beyond…

Early February we presented a talk at FOSDEM, a huge Open-Source gathering with my colleague Alireza Farshin. The video is now released!

In the talk we present FastClick with a short demo, do a round of existing alternative modular framework (VPP and BESS mainly) and then discuss the future of software dataplanes, which we believe our recent work PacketMill starts to address.

We mainly show how FastClick is still really up-to-date with competition and goes beyond sota with PacketMill’s enhancements. We also re-did an experiment at 100G showing how FastClick now improves Click by more than 30x in a forwarding configuration. This is because we continued to maintain FastClick since nearly 6 years now and we do consider pull requests, and integrate recent research while good old Click itself is sadly stalling since a decade now. I will do a blog post about the state of FastClick in the next weeks.

I also bought the www.fastclick.dev domain to start a little showcase website. For now it redirects to GitHub. Feel free to help 🙂

Links : video ; slides ; page

A poster of our latest work, CrossRSS, a Stateless CPU-Aware Datacenter Load-Balancer

Today we will present a poster of our latest work, at CoNEXT’20 : CrossRSS! CrossRSS is a load-balancer that spreads the load uniformly even inside the servers. It uses knowledge of the dispatching done inside the servers, RSS, to purposely select less-loaded cores without any server modification, or inter-core communications on the server. Learn more by watching the short video!

The poster session will be held on the 4th of December, 2:30 CET on the Mozilla VR Hub

Extended Abstract ; Hub ; Video ; Poster-As-Slides

Our latest paper “Cheetah”, a load balancer that guarantees per-connection-consistency

Cheetah is a new load balancer that solves the challenge of remembering which connection was sent to which server without the traditional trade off between uniform load balancing and efficiency. Cheetah is up to 5 times faster than stateful load balancers and can support advanced balancing mechanisms that reduce the flow completion time by a factor of 2 to 3x without breaking connections, even while adding and removing servers.

More information at https://www.usenix.org/conference/nsdi20/presentation/barbette.

Our new paper RSS++: load and state-aware receive side scaling

I’m delighted to announce the publication of our latest paper titled “RSS++: load and state-aware receive side scaling” at CoNEXT’19.


While the current literature typically focuses on load-balancing among multiple servers, in this paper, we demonstrate the importance of load-balancing within a single machine (potentially with hundreds of CPU cores). In this context, we propose a new load-balancing technique (RSS++) that dynamically modifies the receive side scaling (RSS) indirection table to spread the load across the CPU cores in a more optimal way. RSS++ incurs up to 14x lower 95th percentile tail latency and orders of magnitude fewer packet drops compared to RSS under high CPU utilization. RSS++ allows higher CPU utilization and dynamic scaling of the number of allocated CPU cores to accommodate the input load while avoiding the typical 25% over-provisioning.

RSS++ has been implemented for both (i) DPDK and (ii) the Linux kernel. Additionally, we implement a new state migration technique which facilitates sharding and reduces contention between CPU cores accessing per-flow data. RSS++ keeps the flow-state by groups that can be migrated at once, leading to a 20% higher efficiency than a state of the art shared flow table.

Paper ; Video ; Slides

Our latest paper “Metron: NFV Service Chains at the True Speed of the Underlying Hardware” has been accepted at NSDI 2018 !


In this paper we present Metron, a Network Functions Virtualization (NFV) platform that achieves high resource utilization by jointly exploiting the underlying network and commodity servers’ resources. This synergy allows Metron to: (i) offload part of the packet processing logic to the network, (ii) use smart tagging to setup and exploit the affinity of traffic classes, and (iii) use tag-based hardware dispatching to carry out the remaining packet processing at the speed of the servers’ fastest cache(s), with zero intercore communication. Metron also introduces a novel resource allocation scheme that minimizes the resource allocation overhead for large-scale NFV deployments. With commodity hardware assistance, Metron deeply inspects traffic at 40 Gbps and realizes stateful network functions at the speed of a 100 GbE network card on a single server. Metron has 2.75-6.5x better efficiency than OpenBox, a state of the art NFV system, while ensuring key requirements such as elasticity, fine-grained load balancing, and flexible traffic steering.

Paper, slides & video