A context switch looks free until you profile a thread-heavy workload and watch it vanish into the kernel. Here is everything the scheduler actually does to swap one thread for another.
A packet arrives, a key is pressed, a timer fires — and the CPU drops everything, mid-instruction-stream, to run kernel code. How interrupts work, why handlers are split in half, and how NAPI killed the interrupt storm.
The same read() works on ext4 files, /proc fictions, sockets, and pipes because Linux routes every file operation through one dispatch layer. The VFS is the kernel's biggest interface — and its object model is worth stealing.
For 15 years Linux picked the next task with a red-black tree of virtual runtimes. In 6.6 that changed for the first time since 2007. What fairness actually means, how nice values work, and why latency-sensitive tasks forced a redesign.
A function call costs ~2ns. A syscall costs ~100ns before doing any work — and that's after decades of optimization plus a Spectre-era tax. Where the time goes, why vDSO exists, and what that means for API design.
malloc has a supplier: the kernel's own allocators. The buddy system deals in power-of-two page blocks and fights fragmentation with math; the slab layer turns pages into typed object caches. Between them, every allocation on your machine.
The Linux kernel's list_head puts the container inside the object instead of the object inside the container — one implementation, zero allocations, and a container_of macro that looks illegal but isn't. I built a library around the pattern; here's why it wins.
Every pointer dereference triggers a virtual-to-physical translation through a four-level radix tree. The only reason your machine isn't 5x slower is a tiny cache called the TLB — and when it misses, you feel it.
fork clones a 10 GB process in under a millisecond by copying nothing — just page tables, marked read-only. The first write to any page pays the real cost. Elegant, and the source of Redis's most famous operational trap.
