2.4.23 can run with HZ==0!

From: Frank van Maarseveen
Date: Sun Dec 28 2003 - 18:03:51 EST

The first thing I noticed was that a select for .2 seconds seemed to
hang in a python script I was working on that time. I didn't believe it
so I tried some other things including "sleep 1", "usleep 1", stracing
them and it all came down to one conclusion

the clock has stopped

/proc/interrupts confirmed that the clock has stopped:

$ cat /proc/interrupts
CPU0
0: 7745428 XT-PIC timer
1: 2 XT-PIC keyboard
2: 0 XT-PIC cascade
8: 1 XT-PIC rtc
9: 0 XT-PIC via82cxxx, usb-uhci
11: 12106 XT-PIC usb-uhci, usb-uhci, eth0
12: 12079 XT-PIC eth1
14: 8582 XT-PIC ide0
15: 8623 XT-PIC ide1
NMI: 0
LOC: 0
ERR: 0
MIS: 0
$ cat /proc/interrupts
CPU0
0: 7745428 XT-PIC timer
1: 2 XT-PIC keyboard
2: 0 XT-PIC cascade
8: 1 XT-PIC rtc
9: 0 XT-PIC via82cxxx, usb-uhci
11: 12116 XT-PIC usb-uhci, usb-uhci, eth0
12: 12079 XT-PIC eth1
14: 8582 XT-PIC ide0
15: 8623 XT-PIC ide1

notice that network irqs are taking place for eth0 but no timer irqs.

halt, reboot (-f) etc didn't work because they all wanted to sleep. I
had to power cycle. Now HZ is ok (1000) again. HZ has been patched but
that's an unlikely cause (patch attached in case you wonder).

Hardware: VIA CL6000

At the time this happened I was also playing with /dev/ttyS3 lines on
the mobo (static discharge?)

--
Frank
--- linux/include/asm-i386/param.h.hz Mon Aug 18 12:15:42 2003
+++ linux/include/asm-i386/param.h Mon Aug 18 12:26:26 2003
@@ -2,8 +2,9 @@
#define _ASMi386_PARAM_H

#ifndef HZ
-#define HZ 100
+#define HZ 1000
#endif
+#define jiffies_to_clock_t(x) ((x) / (HZ / 100))

#define EXEC_PAGESIZE 4096

--- linux/kernel/sys.c.hz Mon Aug 18 12:15:36 2003
+++ linux/kernel/sys.c Mon Aug 18 12:26:20 2003
@@ -807,10 +807,16 @@
* atomically safe type this is just fine. Conceptually its
* as if the syscall took an instant longer to occur.
*/
- if (tbuf)
- if (copy_to_user(tbuf, &current->times, sizeof(struct tms)))
+ if (tbuf) {
+ struct tms tmp;
+ tmp.tms_utime = jiffies_to_clock_t(current->times.tms_utime);
+ tmp.tms_stime = jiffies_to_clock_t(current->times.tms_stime);
+ tmp.tms_cutime = jiffies_to_clock_t(current->times.tms_cutime);
+ tmp.tms_cstime = jiffies_to_clock_t(current->times.tms_cstime);
+ if (copy_to_user(tbuf, &tmp, sizeof(struct tms)))
return -EFAULT;
- return jiffies;
+ }
+ return jiffies_to_clock_t(jiffies);
}

/*
--- linux/kernel/timer.c.hz Wed Dec 4 11:01:40 2002
+++ linux/kernel/timer.c Mon Aug 18 12:15:42 2003
@@ -472,6 +472,15 @@
else
time_adj += (time_adj >> 2) + (time_adj >> 5);
#endif
+#if HZ == 1000
+ /* Compensate for (HZ==1000) != (1 << SHIFT_HZ).
+ * Add 1.5625% and 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
+ */
+ if (time_adj < 0)
+ time_adj -= (-time_adj >> 6) + (-time_adj >> 7);
+ else
+ time_adj += (time_adj >> 6) + (time_adj >> 7);
+#endif
}

/* in the NTP reference this is called "hardclock()" */
--- linux/fs/proc/array.c.hz 2003-11-30 21:52:24.000000000 +0100
+++ linux/fs/proc/array.c 2003-11-30 21:52:26.000000000 +0100
@@ -362,15 +362,15 @@
task->cmin_flt,
task->maj_flt,
task->cmaj_flt,
- task->times.tms_utime,
- task->times.tms_stime,
- task->times.tms_cutime,
- task->times.tms_cstime,
+ jiffies_to_clock_t(task->times.tms_utime),
+ jiffies_to_clock_t(task->times.tms_stime),
+ jiffies_to_clock_t(task->times.tms_cutime),
+ jiffies_to_clock_t(task->times.tms_cstime),
priority,
nice,
0UL /* removed */,
task->it_real_value,
- task->start_time,
+ jiffies_to_clock_t(task->start_time),
vsize,
mm ? mm->rss : 0, /* you might want to shift this left 3 */
task->rlim[RLIMIT_RSS].rlim_cur,
--- linux/fs/proc/proc_misc.c.hz Mon Aug 18 12:15:26 2003
+++ linux/fs/proc/proc_misc.c Mon Aug 18 13:35:59 2003
@@ -325,18 +325,21 @@
}

proc_sprintf(page, &off, &len,
- "cpu %u %u %u %lu\n", user, nice, system,
- jif * smp_num_cpus - (user + nice + system));
+ "cpu %u %u %u %lu\n",
+ jiffies_to_clock_t(user),
+ jiffies_to_clock_t(nice),
+ jiffies_to_clock_t(system),
+ jiffies_to_clock_t(jif * smp_num_cpus - (user + nice + system)));
for (i = 0 ; i < smp_num_cpus; i++)
proc_sprintf(page, &off, &len,
"cpu%d %u %u %u %lu\n",
i,
- kstat.per_cpu_user[cpu_logical_map(i)],
- kstat.per_cpu_nice[cpu_logical_map(i)],
- kstat.per_cpu_system[cpu_logical_map(i)],
- jif - ( kstat.per_cpu_user[cpu_logical_map(i)] \
+ jiffies_to_clock_t(kstat.per_cpu_user[cpu_logical_map(i)]),
+ jiffies_to_clock_t(kstat.per_cpu_nice[cpu_logical_map(i)]),
+ jiffies_to_clock_t(kstat.per_cpu_system[cpu_logical_map(i)]),
+ jiffies_to_clock_t(jif - ( kstat.per_cpu_user[cpu_logical_map(i)] \
+ kstat.per_cpu_nice[cpu_logical_map(i)] \
- + kstat.per_cpu_system[cpu_logical_map(i)]));
+ + kstat.per_cpu_system[cpu_logical_map(i)])));
proc_sprintf(page, &off, &len,
"page %u %u\n"
"swap %u %u\n"