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SubjectRe: How to know HZ from userspace?
Date
Harald Welte writes:

> Is there any way to read out the compile-time HZ value of the kernel?
>
> I had a brief look at /proc/* and didn't find anything.

Look again, this time with a sick mind. Got your barf bag?
Kubys made me do it.

/****************************************************************/
/***********************************************************************\
* Copyright (C) 1992-1998 by Michael K. Johnson, johnsonm@redhat.com *
* *
* This file is placed under the conditions of the GNU Library *
* General Public License, version 2, or any later version. *
* See file COPYING for information on distribution conditions. *
\***********************************************************************/

/* ...but Albert Cahalan wrote the really evil parts.
MKJ is only guilty for the macro */

/* Sets Hertz equal to the kernel's HZ, as seen in /proc. */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#include <unistd.h>
#include <fcntl.h>

#ifndef HZ
#include <netinet/in.h> /* htons */
#endif

long smp_num_cpus; /* number of CPUs */

#define BAD_OPEN_MESSAGE \
"Error: /proc must be mounted\n" \
" To mount /proc at boot you need an /etc/fstab line like:\n" \
" /proc /proc proc defaults\n" \
" In the meantime, mount /proc /proc -t proc\n"

#define STAT_FILE "/proc/stat"
static int stat_fd = -1;
#define UPTIME_FILE "/proc/uptime"
static int uptime_fd = -1;
#define LOADAVG_FILE "/proc/loadavg"
static int loadavg_fd = -1;
#define MEMINFO_FILE "/proc/meminfo"
static int meminfo_fd = -1;

static char buf[1024];

/* This macro opens filename only if necessary and seeks to 0 so
* that successive calls to the functions are more efficient.
* It also reads the current contents of the file into the global buf.
*/
#define FILE_TO_BUF(filename, fd) do{ \
static int local_n; \
if (fd == -1 && (fd = open(filename, O_RDONLY)) == -1) { \
fprintf(stderr, BAD_OPEN_MESSAGE); \
fflush(NULL); \
_exit(102); \
} \
lseek(fd, 0L, SEEK_SET); \
if ((local_n = read(fd, buf, sizeof buf - 1)) < 0) { \
perror(filename); \
fflush(NULL); \
_exit(103); \
} \
buf[local_n] = '\0'; \
}while(0)

unsigned long Hertz;
static void init_Hertz_value(void) __attribute__((constructor));
static void init_Hertz_value(void){
unsigned long user_j, nice_j, sys_j, other_j; /* jiffies (clock ticks) */
double up_1, up_2, seconds;
unsigned long jiffies, h;
smp_num_cpus = sysconf(_SC_NPROCESSORS_CONF);
if(smp_num_cpus==-1) smp_num_cpus=1;
do{
FILE_TO_BUF(UPTIME_FILE,uptime_fd); sscanf(buf, "%lf", &up_1);
/* uptime(&up_1, NULL); */
FILE_TO_BUF(STAT_FILE,stat_fd);
sscanf(buf, "cpu %lu %lu %lu %lu", &user_j, &nice_j, &sys_j, &other_j);
FILE_TO_BUF(UPTIME_FILE,uptime_fd); sscanf(buf, "%lf", &up_2);
/* uptime(&up_2, NULL); */
} while((long)( (up_2-up_1)*1000.0/up_1 )); /* want under 0.1% error */
jiffies = user_j + nice_j + sys_j + other_j;
seconds = (up_1 + up_2) / 2;
h = (unsigned long)( (double)jiffies/seconds/smp_num_cpus );
/* actual values used by 2.4 kernels: 32 64 100 128 1000 1024 1200 */
switch(h){
case 30 ... 34 : Hertz = 32; break; /* ia64 emulator */
case 48 ... 52 : Hertz = 50; break;
case 58 ... 62 : Hertz = 60; break;
case 63 ... 65 : Hertz = 64; break; /* StrongARM /Shark */
case 95 ... 105 : Hertz = 100; break; /* normal Linux */
case 124 ... 132 : Hertz = 128; break; /* MIPS, ARM */
case 195 ... 204 : Hertz = 200; break; /* normal << 1 */
case 253 ... 260 : Hertz = 256; break;
case 393 ... 408 : Hertz = 400; break; /* normal << 2 */
case 790 ... 808 : Hertz = 800; break; /* normal << 3 */
case 990 ... 1010 : Hertz = 1000; break; /* ARM */
case 1015 ... 1035 : Hertz = 1024; break; /* Alpha, ia64 */
case 1180 ... 1220 : Hertz = 1200; break; /* Alpha */
default:
#ifdef HZ
Hertz = (unsigned long)HZ; /* <asm/param.h> */
#else
/* If 32-bit or big-endian (not Alpha or ia64), assume HZ is 100. */
Hertz = (sizeof(long)==sizeof(int) || htons(999)==999) ? 100UL : 1024UL;
#endif
fprintf(stderr, "Unknown HZ value! (%ld) Assume %ld.\n", h, Hertz);
}
}
/****************************************************************/





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