SMP

SMP (Symmetric Multi-Processing)

See also: Architecture, Process Management, Drivers

Overview

• Max CPUs: 8 (MAX_CPUS)
• Detection: CPUID leaf 1 or leaf 0x80000008
• APIC mode: Local + I/O APIC
• AP state: All APs park in cli; hlt

Bringup sequence

1. smp_init() records BSP as CPU 0, detects AP count
2. For each AP: sends INIT IPI → waits 10 ms → sends SIPI to 0x8000 (trampoline)
3. AP starts in real mode, climbs to long mode via the trampoline
4. AP calls ap_main(cpu_id) which records its APIC id via CPUID and parks

Trampoline (trampoline.asm)

Position-independent real-mode stub compiled as flat binary and embedded via ld -r -b binary. Sets up segments, A20, protected mode, long mode, then jumps to ap_main.

CPU topology (cpus command)

SMP: 4 CPU(s) online (max 8)
CPU  ROLE  APIC  SELF  STATE
0    BSP   0     0     online
1    AP    1     1     online
2    AP    2     2     online
3    AP    3     3     online

Per-CPU data

typedef struct {
    uint32_t apic_id;       // assigned by BSP
    uint32_t apic_id_self;  // read by core via CPUID
    uint32_t cpu_number;
    uint64_t stack_base;
    uint64_t stack_top;
    volatile int started;
    volatile int running;
} cpu_info_t;

Future work

• Per-CPU run queues, reschedule IPIs, TLB shootdown, spinlocks, IRQ affinity