On 11-12-07 15:15, Rene Herman wrote:
On 11-12-07 14:32, Paul Rolland wrote:
On 11-12-07 13:08, David Newall wrote:
Rene Herman wrote:
(*) some local testing shows it to be almost exactly that for both
out and in on my own PC -- a little over. If anyone cares, see
attached little test program. The "little over" I don't worry about.
0 us delay is also fine for me and if any code was _that_ fragile it
would have broken long ago.
Some results :
Okay, these vary to wildly for you and might I suppose be a serialising
artifact or some such. Give me a bit and I'll try to improve it...
This might be a bit more constant, I suppose. This serialises with cpuid.
Don't see a difference locally, but perhaps you do.
On a Duron 1300 with an actual ISA bus, "out" is between 1300 and 1600 for
me and "in" between 1200 and 1500 with a few flukes above that which will I
suppose be caused by the bus (ISA _or_ PCI) being momentarily busy or some
such...
Rene.
#include <stdlib.h>
#include <stdio.h>
#include <sys/io.h>
#define LOOPS 1000
unsigned long cycles[LOOPS];
int main(void)
{
unsigned long overhead;
unsigned long total;
int i;
if (iopl(3) < 0) {
perror("iopl");
return EXIT_FAILURE;
}
/* pull it in */
for (i = 0; i < LOOPS; i++)
cycles[i] = 0;
asm volatile ("cli");
for (i = 0; i < LOOPS; i++)
asm (
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"movl %%eax, %%esi \n\t"
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"subl %%esi, %%eax \n\t"
: "=a" (cycles[i]) : : "ecx", "edx", "ebx", "esi");
asm volatile ("sti");
overhead = 0;
for (i = 0; i < LOOPS; i++)
overhead += cycles[i];
asm volatile ("cli");
for (i = 0; i < LOOPS; i++)
asm (
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"movl %%eax, %%esi \n\t"
"outb %%al, $0x80 \n\t"
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"subl %%esi, %%eax \n\t"
: "=a" (cycles[i]) : : "ecx", "edx", "ebx", "esi");
asm volatile ("sti");
total = 0;
for (i = 0; i < LOOPS; i++)
total += cycles[i];
total -= overhead;
printf("out: %lu\n", total / LOOPS);
asm volatile ("cli");
for (i = 0; i < LOOPS; i++)
asm (
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"movl %%eax, %%esi \n\t"
"inb $0x80, %%al \n\t"
"xor %%eax, %%eax \n\t"
"cpuid \n\t"
"rdtsc \n\t"
"subl %%esi, %%eax \n\t"
: "=a" (cycles[i]) : : "ecx", "edx", "ebx", "esi");
asm volatile ("sti");
total = 0;
for (i = 0; i < LOOPS; i++)
total += cycles[i];
total -= overhead;
printf("in : %lu\n", total / LOOPS);
return EXIT_SUCCESS;
}
