Welcome, byte manglers, buffer wranglers, and syscall whisperers.

This is Hacker Wisdom – a multi-part series distilling decades of blood, sweat, segfaults, and premature optimizations from the minds of true kernel hackers, network engineers, and systems freaks. No fluff, no high-level nonsense, just hard-earned truths from the lower layers. The parts of the stack you only discover when the abstractions betray you.

This series isn't about "learning to code". This is about understanding the machine.

Lesson 1: Syscalls Are Latency Portals

Every time you enter the kernel, you owe it your time.
– Tarkan, systems architect, wakes up thinking in epoll

In userland, a function call is practically free. But the moment you hit a syscall, you cross a boundary. CPU state changes, privilege level flips, TLBs shake, caches shiver, locks creak.

You're not calling a function. You're stepping into an ancient temple, and the priest (scheduler) might not let you out until he feels like it.

Protip: Use strace like a stethoscope. Listen for syscall chatter. Silence is speed.

Lesson 2: Memory You Don't Touch Is the Fastest of All

"A zero-copy path is worth ten optimizations."
– Zoya, network packet ninja, 4 AM, debugging a 1Gbps ↔ 100Gbps bridge

Every time you copy memory, you pay. Not just in instructions – in cache pollution, in NUMA misses, in TLB evictions. Zero-copy isn't a trick. It's a religion.

True hackers chase linear ownership transfer: from disk to socket, from user buffer to DMA bus, with no middlemen.

Protip: Know your mmap(), splice(), sendfile(), vmsplice() and how they cheat the system.

Lesson 3: The Kernel Doesn't Care About Your Feelings

If your process is unresponsive, it's not the kernel's fault. It's yours.
– V, ex-Linux scheduler maintainer, known to profile with perf on first dates

The kernel does not love you. It schedules fairly. Or tries to. Your job is to understand the rules and bend them without breaking them.

Use mlock() to pin memory. Use CPU affinity to hog cores. Use cgroups to cordon off noisy neighbors. Learn sched_setaffinity, nice, and ionice like other people learn yoga.

Protip: If you want predictability, make it yourself. Don't beg the kernel to do it.

Lesson 4: IO Is a Giant Lie

"Async is fake unless you run threads or poll rings."
– Nameless network stack engineer, burned out rewriting TLS for the 3rd time

Blocking I/O is easy. Async I/O is a trap. True async with predictable latency, backpressure, and throughput is built atop epoll/uring/thread pools. Everything else is an illusion with await sprinkled on top.

Protip: Learn how the event loop really works. And know when to cheat with threads.

Lesson 5: Benchmarks Lie — Until You Write Your Own

"There is no general performance. Only performance in your exact workload."
– Eri, embedded systems profiler, surgically removed 13 memcpys from a path

Your program doesn't run in a vacuum. It runs in a context: CPU topology, kernel version, SSD vs. HDD, VM vs. bare metal, containerized or not. Benchmarks on StackOverflow are for decoration.

Write your benchmarks. Tiny, tight loops that test what matters: syscall cost, memory layout, concurrency models.

Protip: Use perf, time, vmstat, numactl, taskset, and rdtsc like a jazz musician plays scales.

Coming Up in Part II

  • Memory alignment is not optional
  • Network stacks: you are the bottleneck
  • Understanding page faults is your first step toward enlightenment
  • How ptrace can teach you everything
  • System call hoarding: a survival guide

Update: Part II is live!

If you're a true system junkie, the kind who stares at /proc for fun and dreams of lock-free queues, then this series is for you.

Drop a comment if you've got your own battle scars or if there's a piece of wisdom we should immortalize.

Stay tuned for Part II, and until then – keep hacking close to the metal.

P.S. Want a printable version in ASCII, LaTeX, or hex-dump? Let me know.