RT demo — user-space lab (Lectures 1–9)

Small Linux program that illustrates ideas from the first nine OS lectures: processes and threads, syscalls, scheduling (SCHED_FIFO), CPU affinity, memory locking / pre-faulting, and pthread synchronization.

Kernel-side topics (interrupts, boot, modules, device tree) are only described in comments or below—not implemented here.

Build and run

From this directory:

cd "Phase 1 - Foundational Knowledge/3. Operating Systems/Lectures/demos/rt-demo"
make
./rt_demo [options]

Without make: gcc -Wall -O2 -pthread -o rt_demo rt_demo.c

Options: ./rt_demo --help — e.g. --cpu 2,3, --rt (needs root / cap_sys_nice), --lock-memory (needs root / cap_ipc_lock), --no-rt.

Trace syscalls: strace -e sched_setscheduler,sched_setaffinity,mlockall,gettid,clock_gettime ./rt_demo --rt --cpu 1 2>&1 | head -50

Lecture mapping

Lecture	Topic	In this demo
L1	OS as resource manager; user vs kernel	Runs in user space; uses syscalls to request kernel services
L2	Process / threads	main() + worker thread; getpid(), gettid(), affinity
L3	Interrupts, top/bottom half	Event-style wakeup only; real IRQs are kernel/driver
L4	System calls	sched_setscheduler, sched_setaffinity, mlockall, clock_gettime, …
L5	Boot, modules, device tree	Not in code; see L5 on a real machine below
L6	Scheduling	sched_setscheduler(SCHED_FIFO)
L7	RT Linux, latency	mlockall(), pre-faulting, no alloc in hot loop
L8	Affinity & isolation	sched_setaffinity()
L9	Synchronization	pthread_mutex_t, pthread_rwlock_t, pthread_cond_t

L5 on a real machine

• Boot: dmesg at boot; systemd-analyze
• Modules: lsmod, modinfo, modprobe (e.g. loop)
• Device tree (ARM): /sys/firmware/devicetree/base/ or machine model in boot logs

Requirements

Linux or WSL with pthreads and sched.h. --rt / --lock-memory usually require root or the matching capabilities.

Files

File	Purpose
rt_demo.c	Source
Makefile	Build
README.md	This file

Back to the section hub: Operating Systems Guide.

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