how to get cpu_khz?

how to get cpu_khz?

[David Fries]

I'm using the TSC of the Pentium processors to get some precise timing
delays for writing to a eeprom (bit banging bus operations), and it
works just fine, but the cpu_khz variable isn't exported to a kernel
module, so I hardcoded in my module.  It works fine for that one
system, but obviously I don't want to hard code it for the general
case.  I guess I could write my own routine to figure out what the
cpu_khz is, but it is already done, so how do I get access to it?

-- 
		+---------------------------------+
		|      David Fries                |
		|      dfries@mail.win.org        |
		+---------------------------------+

Re: how to get cpu_khz?

[Alan Cox]

> > calculated at boot time (that's where /proc/cpuinfo gets its data) and
> > that variable doesn't appear to be exported to the rest of the kernel,
> > either that or I'm just missing something, which I would rather be the
> > case at this point.
> > 
> 
> Ask Alan to export it by default. If no-go, export it in your
> configuration.

Processor speed from cpu_khz is not a constant, it varies per processor
on split multiplier SMP and it varies on certain kinds of power management.
For delays we have udelay(). That has a chance of supporting speed changes

Re: how to get cpu_khz?

[Richard B. Johnson]

On Mon, 17 Sep 2001, David Fries wrote:

> On Mon, Sep 17, 2001 at 03:11:26PM -0400, John Weber wrote:
> > David Fries wrote:
> > > 
> > > I'm using the TSC of the Pentium processors to get some precise timing
> > > delays for writing to a eeprom (bit banging bus operations), and it
> > > works just fine, but the cpu_khz variable isn't exported to a kernel
> > > module, so I hardcoded in my module.  It works fine for that one
> > > system, but obviously I don't want to hard code it for the general
> > > case.  I guess I could write my own routine to figure out what the
> > > cpu_khz is, but it is already done, so how do I get access to it?
> > 
> > I don't know of any official way of doing this, but here's some 
> > code (written by aa) that accomplishes this.
> 
> For a user space program you could just read /proc/cpuinfo, I'm
> actually writing a kernel driver, maybe I wasn't clear enough.  I'm
> just frustrated because the variable I'm after, cpu_khz is already
> calculated at boot time (that's where /proc/cpuinfo gets its data) and
> that variable doesn't appear to be exported to the rest of the kernel,
> either that or I'm just missing something, which I would rather be the
> case at this point.
> 

Ask Alan to export it by default. If no-go, export it in your
configuration.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).

    I was going to compile a list of innovations that could be
    attributed to Microsoft. Once I realized that Ctrl-Alt-Del
    was handled in the BIOS, I found that there aren't any.

Re: how to get cpu_khz?

[David Fries]

On Mon, Sep 17, 2001 at 03:11:26PM -0400, John Weber wrote:
> David Fries wrote:
> > 
> > I'm using the TSC of the Pentium processors to get some precise timing
> > delays for writing to a eeprom (bit banging bus operations), and it
> > works just fine, but the cpu_khz variable isn't exported to a kernel
> > module, so I hardcoded in my module.  It works fine for that one
> > system, but obviously I don't want to hard code it for the general
> > case.  I guess I could write my own routine to figure out what the
> > cpu_khz is, but it is already done, so how do I get access to it?
> 
> I don't know of any official way of doing this, but here's some 
> code (written by aa) that accomplishes this.

For a user space program you could just read /proc/cpuinfo, I'm
actually writing a kernel driver, maybe I wasn't clear enough.  I'm
just frustrated because the variable I'm after, cpu_khz is already
calculated at boot time (that's where /proc/cpuinfo gets its data) and
that variable doesn't appear to be exported to the rest of the kernel,
either that or I'm just missing something, which I would rather be the
case at this point.

-- 
		+---------------------------------+
		|      David Fries                |
		|      dfries@mail.win.org        |
		+---------------------------------+

Re: how to get cpu_khz?

[John Weber]

[-- Attachment #1: Type: text/plain, Size: 619 bytes --]

David Fries wrote:
> 
> I'm using the TSC of the Pentium processors to get some precise timing
> delays for writing to a eeprom (bit banging bus operations), and it
> works just fine, but the cpu_khz variable isn't exported to a kernel
> module, so I hardcoded in my module.  It works fine for that one
> system, but obviously I don't want to hard code it for the general
> case.  I guess I could write my own routine to figure out what the
> cpu_khz is, but it is already done, so how do I get access to it?

I don't know of any official way of doing this, but here's some 
code (written by aa) that accomplishes this.

[-- Attachment #2: MHz.c --]
[-- Type: text/plain, Size: 1277 bytes --]

/*
 *  $Id: MHz.c,v 1.4 2001/05/21 18:58:01 davej Exp $
 *  This file is part of x86info.
 *  (C) 2001 Dave Jones.
 *
 *  Licensed under the terms of the GNU GPL License version 2.
 *
 * Estimate CPU MHz routine by Andrea Arcangeli <andrea@suse.de>
 * Small changes by David Sterba <sterd9am@ss1000.ms.mff.cuni.cz>
 *
 */

#include <stdio.h>
#include <sys/time.h>
#include <string.h>
#include <unistd.h>

__inline__ unsigned long long int rdtsc()
{
	unsigned long long int x;
	__asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
	return x;
}

void estimate_MHz()
{
	struct timezone tz;
        struct timeval tvstart, tvstop;
        unsigned long long int cycles[2]; /* gotta be 64 bit */
	unsigned int microseconds; /* total time taken */
	
	memset(&tz, 0, 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 */
	usleep(1000000);
	
	cycles[1] = rdtsc();
	gettimeofday(&tvstop, &tz);
	microseconds = ((tvstop.tv_sec-tvstart.tv_sec)*1000000) +
		(tvstop.tv_usec-tvstart.tv_usec);

	printf("%lldMHz processor (estimate).\n",
		(cycles[1]-cycles[0])/microseconds);
}

int main(void)
{
	while (1) {
		estimate_MHz();
	}
	return (0);
}