For your eyes,
while reading this thread I wrote a sample program to test if the clock
sometimes goes backward/forward.
I started my program while continuing reading threads on the linux-kernel
archive. After about 90 minutes of continuous running I went back to the window
running the program and surprise I saw this:
$ ./tloop
Bump negative -4294967295
^C
Summary:
-------
Min = 0
Max = 257845
Avg = 1 (6009092476/5521919279)
So it looks like the time changed somewhere of a value +/- 4,295 seconds.
kernel 2.4.18
$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 8
model name : Pentium III (Coppermine)
stepping : 1
cpu MHz : 602.566
cache size : 256 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips : 1202.58
--------------------- program tloop.c -------------------------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/time.h>
#include <signal.h>
typedef long long LL;
LL GetTime (void)
{
struct timeval tv;
LL retval;
gettimeofday (&tv, NULL);
retval = (tv.tv_sec * 1000000) + (tv.tv_usec);
return retval;
}
volatile int Break = 0;
void Trap (int sig)
{
Break = 1;
}
int main (void)
{
LL Now, Old;
LL Dt, Min=9999999, Max=0, Num=0, Tot=0;
Old = Now = GetTime ();
signal (SIGINT, Trap);
signal (SIGQUIT, Trap);
for ( ; Break==0 ; )
{
Now = GetTime();
if (Now < Old)
{
printf ("Bump negative %lld\n", (Now-Old));
}
else
{
Dt = Now-Old;
Min = (Dt < Min) ? Dt : Min;
Max = (Dt > Max) ? Dt : Max;
Tot += Dt;
Num += 1;
}
Old = Now;
}
printf ("Summary:\n-------\n Min = %lld\n Max = %lld\n "
"Avg = %lld (%lld/%lld)\n", Min, Max, Tot/Num, Tot, Num);
return 0;
}
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This archive was generated by hypermail 2b29 : Sun Jun 30 2002 - 22:00:08 EST