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Multi-core networking in Linux user space with zero overhead

Posted: 02 Jul 2012 ?? ?Print Version ?Bookmark and Share

Keywords:accelerators? application software? Partitioning?

One thing common to all data plane processing is handling of statistics. Statistics counters such as byte and packet counters and application specific counters often need to be kept per flow, and also per higher abstraction levels as required by applications. Therefore a large number of counters can be expected in higher end devices.

Since multicore synchronized access to shared counters are costly, a multicore SoC can also provide a statistics acceleration mechanism C one that would make incrementing statistics for millions of counters very efficient.

Once a packet is processed through all necessary application modules in the data plane, the packet is sent out to the egress interface. Typical processing here requires scheduling and shaping (or rate limiting). Since standard QoS algorithms are generally used, these functions can also be offloaded to hardware units, so that the application modules need only enqueue packets to egress processing units.

Zero-overhead user space network software framework
Multi-core SoCs software developers have been challenged with writing applications that suit specific SoC families and their derivatives. This means writing specialized code that is suitable and specific to a given SoC.

For example queuing, buffer management, statistics, accelerators and other technologies would have very specific modus operandi that applications must follow. There would also be specific methods of interfacing with the hardware to receive and send packets, and for distributing work.

These also result in application software architecture being dictated to some extent by the SoC. Migrating software across SoCs, even within the family of the same SoC product line can be a large and expensive development effort, and a burden on maintenance and support.

There is a need for a software framework that is able to leverage features provided by a multicore SoC, without the need for in-depth expertise in the hardware operational understanding.

Applications need to be portable, and be able to leverage different SoCs and families without software application changes, essentially through configuration of features and an abstracted execution environment.

Much like a traditional (i.e. non-embedded) operating system that hides many hardware details from applications, a network software framework that hides SoC specific details and offers a consistent programming model to applications is the need of the hour.

Limits of Linux in the dataplane
Direct use of Linux kernel for data plane implementations has limitations. Linux kernels provide abstraction for disk I/O, USB, processor features and other hardware elements. However, scaling to millions of flows/sessions in datapath is not easy in the Linux kernel space. Kernel resident applications suffer from limited memory, an environment that is hard to develop and debug in. Vendors also have GPL concerns with Linux kernel modules.

In order to overcome the limitations of Linux, it is required to execute applications in user-space with virtually zero-overhead and with direct access to the SoC hardware, and provide a software framework, which caters to various needs of networking applications without requiring knowledge of hardware specific details.

Such a framework needs to support layer 2, layer 3 and higher layer processing, orchestrate packet flow, manage packet buffers, provide access to hardware accelerators, timers, and statistics.

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