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SubjectUtilizing rdtsc on i586?
I made the following module to try out the Pentium cycle counter,
but I believe it's broken. For one thing, it seems to cause random
processes to segfault upon loading (at least, it did this before adding
the cli()/sti() around the main code... not sure if it would do it
anymore). For another, it returns 67 cycles
for a for loop that [according to the assembly output] should take
about 20. It returns around 5000 cycles if the index starts out as
1000. (I have a p100)

Hope there's a kind soul out there willing to point out my mistakes,
or why this has anomalous output.

[cut here]
#include <linux/config.h>
#include <linux/module.h>
#include <asm/system.h>
#include <asm/segment.h>
#include <asm/uaccess.h>
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/timer.h>
#include <linux/malloc.h>

#ifdef MODULE

int init_module(void)
{
unsigned int cnt3, cnt2, cnt1;
int i;
printk("cc: started... ");
cli();
__asm__(".byte 0x0f,0x31" : "=a" (cnt1), "=d" (cnt3));
/* put code to time here */
for(i=0;i<10;i++);
/* end code to time here */
__asm__(".byte 0x0f,0x31" : "=a" (cnt2), "=d" (cnt3));
sti();
printk(" operation took %d cycles\n", cnt2-cnt1);
return 0;
}
void cleanup_module(void)
{
}
#endif
[cut here]
--
_ ____ Joe Fouche (jf@ugcs.caltech.edu)
___| |--- Deranged College Student
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