On Thu, Jan 10, 2008 at 02:31:46PM +0530, amit mehta wrote:
> One of our customer is facing an issue with jiffies wrap up.
> on a 32 bit machine, the variable jiffies count upto 472 days.
> the customer's server was up for 472 days ('uptime') and to reproduce
> the same, i tried to tweak with the variable HZ in
> linux-2.6..23.9/include/asm-i386/param.h
> but it seems that it is not working(i may be doing something stupid as well)
Problems with jiffies wrapup shouldn't happen with 2.6 kernels anymore
because jiffies is initialised at a couple of minutes before wrap up.
That shook out quite some jiffies wrap up bugs.
> i changed HZ from 100 to 10000 in linux-2.6..23.9/include/asm-i386/param.h .
Better do it in kernel/Kconfig.hz
> Then after rebuilding the kernel.and booting from it
> i inserted a small module to read the jiffies and HZ global variable( i
> don't know if there is any user level command to read the same) ,which is as
> follows:
>
> [root@localhost drivers]# cat get_jiffies.c
> #include <linux/init.h>
> #include <linux/module.h>
> #include <asm/current.h>
> #include <linux/sched.h>
> #include <linux/time.h>
> #include <linux/jiffies.h>
> static int __init jiffies_init(void)
> {
> unsigned long j,z;
> j = z = 0;
> j = jiffies;
> z = HZ;
> printk(KERN_ALERT "jiffies value is %lu\n",j);
> printk(KERN_ALERT "jiffies value in seconds %lu\n",(jiffies/HZ));
> printk(KERN_ALERT "HZ value is %lu\n",z);
> return 0;
> }
>
> static void __exit jiffies_exit(void)
> {
> printk(KERN_ALERT "Goodbye, world!\n");
> }
>
> module_init(jiffies_init);
> module_exit(jiffies_exit);
>
> MODULE_LICENSE("GPL");
>
> [root@localhost drivers]# insmod get_jiffies.ko
> [root@localhost drivers]# dmesg
> jiffies value is 372939
> jiffies value in seconds 1491
> HZ value is 250 <====
>
> why this HZ variable is shown as 250 ?
Because it is overridden from kernel/Kconfig.hz .
Erik
--
They're all fools. Don't worry. Darwin may be slow, but he'll
eventually get them. -- Matthew Lammers in alt.sysadmin.recovery
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