Where time goes — kernel networking, syscalls, context switches

The Per-Packet Tax

When a packet arrives at a NIC and follows the standard Linux kernel path, several operations happen on the way to user space. The NIC raises an interrupt or DMAs the packet into a memory ring. The kernel allocates an sk_buff structure to wrap the packet metadata. The driver hands the packet to the network stack which determines whether it is destined for a local socket or routed elsewhere. Protocol parsing extracts L3 and L4 headers. Routing lookup finds the destination socket. The socket layer copies the payload into a user-space buffer. The application is woken from its sleep on read().…