Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

[Rene Herman <rene.herman@keyaccess.nl>]

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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.

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#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;
}