Re: How to measure flow of time using Time Stamp Counter on i386machines

[linux-os]

On Thu, 9 Dec 2004, krishna wrote:

> Hi all,
>
>   Can anyone tell me how to measure flow of time using Time Stamp Counter on 
> pentium machines.
>   Which documentation could help me in understanding it.
>
> Regards,
> Krishna Chaitanya
> -

The rdtsc instruction returns the CPU clocks that have occurred
since the time the machine was started. If you assemble the
provided code as:

as -o tim.o tim.S

... then link this with your code, it will return the CPU clocks
that have occurred between two successive calls..

extern long long tim(void);

code()
{
    long long total;

    (void)tim();         // Initialize
    do_something();      // Some code to measure
    total = tim();       // Get measurement

   printf("Total CPU clocks are %lld\n", total);

}


-------------
#
#	This is free software written by Richard B. Johnson. No
#	copyright is claimed. It is also not guaranteed to do anything
#	useful.
#
#

.data
lastl:	.long	0
lasth:	.long	0
.text
.align	8 
.globl	tim
.type 	tim@function

#
#  Return the CPU clock difference between successive calls.
#
tim:	pushl	%ebx
	rdtsc
	movl	(lastl), %ebx		# Get last low longword
	movl	(lasth), %ecx		# Get last high longword
	movl	%eax, (lastl)		# Save current low longword
	movl	%edx, (lasth)		# Save current high longword
	subl	%ebx, %eax		# Current - last
	sbbl	%ecx, %edx		# Same with borrow
	popl	%ebx
	ret
.end
--------------------



Cheers,
Dick Johnson
Penguin : Linux version 2.6.9 on an i686 machine (5537.79 BogoMips).
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