🔒 Locked

Clock cycle counting?

Started by c0nfUzEd Nov 28, 2001 at 7:22 PM 1 replies 350+ views

Original Post

c0nfUzEd

Nov 28, 2001 at 7:22 PM

If I have some asm code, how can I count the number of clock cycles it takes?

Shannon Barber

Nov 28, 2001 at 11:07 PM

RDTSC is an 586+ opcode that puts the current CPU tick into edx:eax

  
__int64 __declspec( naked )  RDTSC()
	{
	_asm
		{
		//Prolog

		push   ebp
      mov    ebp, esp
      sub    esp, __LOCAL_SIZE
      
		//Get CPU Ticks

		cpuid
		//_emit  0x0f				// CPUID

		//_emit  0xa2

		rdtsc
		//_emit  0x0f				// RDTSC

		//_emit  0x31



		//Epilog

      mov    esp, ebp
      pop    ebp
		ret
		}
	}

If you have the processor pack it will recongize rdtsc and cpuid, otherwise you need to use the _emit directive.

This isn''t the best way to it, but it''s a start. Ideally you''d want to inline the cpuid and rdtsc opcodes and move the edx:eax result to where you want to store it.

c0nfUzEd

Nov 29, 2001 at 3:16 AM

Thanks, it worked in MSVC, but I also wanted to use it in DJGPP. I looked around and found this:

  
long long readTSC (void)
{
  long long t;
  asm (".byte 0x0f,0x31"  /* opcode 0x0f31 */
       : "=A" (t)         /* output parameters : edx:eax -> t */
       :                  /* no input register */
       : "%eax", "%edx"); /* registers destroyed in asm */
  return t;      
}

But the compiler says "''asm'' needs too many reloads". Does anyone know what this means and how to fix it?

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.