Measuring context switches :: a small expedition. Part I

First up some assembler code. It just works for i386 currently. The first routine gives me the core number the code is currently executing under (see Intel Application Note 485 for more details)

   .text
   .globl __apicID
__apicID:
   push     %ebx

   movl     $0x1,%eax
   cpuid

   mov      %ebx, %eax
   shr      $24,%eax

   popl     %ebx
   
   ret

and the second function returns the number of cycles elapsed since power on

   .text
.globl __rdtsc
__rdtsc:
        rdtsc
        ret

I haven't coded i386 assembler much, it probably shows :)