[root@metallica /root]# ./mhz.estimate
Illegal Instruction (core dumped)
Now, does this program only work on pentium's, i'm a little confused.
-Robg
On Sat, 27 Dec 1997, Robert Woodcock wrote:
> Phile Brutsche wrote:
> >On another note, I just looked at your patch. It uses the rdtsc
> >instruction; this instruction does not exist on anything less than a
> >Pentium. I'm not sure what the kernel would do on '486 or '386, but it
> >would'nt be pretty. A better solution for this would be to time the bsf
> >instruction on those chips. I have source in C and assembly if you need
> >help.
>
> Can you mail that to me at the return address?
>
> Currently I'm using this userspace code I pieced together myself (well,
> not the rdtsc function, I ripped that from the I/O Port Programming HOWTO)
> which is so consistent that it's making me wonder if my motherboard clock
> chip is a little bit off and is actually running my CPU at 99.57mhz
> instead of 100. (I gave this program to several other people with pentiums
> and it seems to consistently report either high and low depending on the
> system.)
>
> mercury:~$ (while :; do mhz.estimate; done)
> 99.569984 MHz processor.
> 99.569979 MHz processor.
> 99.570001 MHz processor.
> 99.569946 MHz processor.
>
> Kinda makes you wonder about those motherboard benchmarks where all the
> motherboards are within a few tenths of a percent of each other. :)
>
> Compile as usual, gcc mhz.estimate.c -o mhz.estimate.
>
> #include <stdio.h>
> #include <sys/time.h>
>
> /* returns number of clock cycles since last reboot */
> __inline__ unsigned long long int rdtsc()
> {
> unsigned long long int x;
> __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
> return x;
> }
>
> main ()
> {
> struct timezone tz;
> struct timeval tvstart, tvstop;
> unsigned long long int cycles[2]; /* gotta be 64 bit */
> unsigned int microseconds; /* total time taken */
>
> bzero(&tz, sizeof(tz));
>
> /* get this function in cached memory */
> gettimeofday(&tvstart, &tz);
> cycles[0] = rdtsc();
> gettimeofday(&tvstart, &tz);
>
> /* we don't trust that this is any specific length of time */
> sleep(1);
>
> cycles[1] = rdtsc();
> gettimeofday(&tvstop, &tz);
> microseconds = ((tvstop.tv_sec-tvstart.tv_sec)*1000000) +
> (tvstop.tv_usec-tvstart.tv_usec);
>
> printf("%f MHz processor.\n",
> (float)(cycles[1]-cycles[0])/microseconds);
> }
> --
> Robert Woodcock - robert@olex.com
> All I want is a warm bed and a kind word and unlimited power.
> -- Ashleigh Brilliant
>