syscall-timing.asm

global start
global _main
extern _printf

%define SYSCALL_COUNT_EXPONENT 20
%define SYSCALLS_PER_ITERATION 4

fmt_lld db "%lld", 10, 0

_main:
    sub rsp, 8

    mov r15, (1 << SYSCALL_COUNT_EXPONENT) / SYSCALLS_PER_ITERATION

    rdtsc
    shl rdx, 32
    or rax, rdx
    mov r14, rax

    .begin:
        %rep SYSCALLS_PER_ITERATION
            mov rax, 0x2000000 | 20 ; getpid
            syscall
        %endrep

        dec r15
        test r15, r15
        jnz .begin

    rdtsc
    shl rdx, 32
    or rax, rdx
    sub rax, r14

    shr rax, SYSCALL_COUNT_EXPONENT

    mov rdi, fmt_lld
    mov rsi, rax
    call _printf

    xor rax, rax
    add rsp, 8
    ret