linux kernel

Reasons for Bottom Half Handlers

Interrupt handlers are nonpreemptible and non-reentrant. However, because the CPU is so limited in what it can do, the nonpreemptible design has potentially.

serious effects on performance by the kernel as well as the processes waiting to be served by the CPU.
Therefore, the work done by interrupt handlers should be as quick as possible. The amount of processing needed by the interrupt handlers during interrupt context depends on the type of event.

if the kernel or a user-space process has to be delayed or preempted, no data will be lost (with the exception of real-time systems, which entail a completely different way of handling processes as well as interrupts). In light of these considerations, modern interrupt handlers are divided into a top half and a bottom half. The top half consists of everything that has to be executed before releasing the CPU, to preserve data. The bottom half contains everything that can be done at relative leisure.

The general requirements of network processor.

Performance: NPs are able to perform many applications at wire speed. Network processors must be able to support high bandwidth connections, multiple protocols, and advanced features without becoming a performance bottleneck.

Flexibility and programmability: Having software as a major part of the system allows network equipment to easily adapt to changing standards and applications.