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Full Discussion: kernel:how to modify and read the tick rate:HZ
Operating Systems Linux kernel:how to modify and read the tick rate:HZ Post 302156391 by amit4g on Tuesday 8th of January 2008 04:20:17 AM
Old 01-08-2008
kernel:how to modify and read the tick rate:HZ
hi,

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 change the variable HZ in linux-2.6..23.9/include/asm-i386/param.h
from 100 to 10000.
after which i rebuilt the kernel with following steps:
# make oldconfig
# make modules_install
# make install

Now when i boot from this newly built kernel, i wrote a small kernel module
to read the jiffies and HZ global variable,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 ?
i am a newbie in kernel programming and i might be doing something really stupid as well.


~amit
 

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LEARN ABOUT HPUX

strmsgsz

STRMSGSZ(5)							File Formats Manual						       STRMSGSZ(5)

NAME

       STRMSGSZ - maximum size of streams message data (bytes)

VALUES

   Failsafe
   Default
   Allowed values
   Recommended values
DESCRIPTION

       This  tunable  limits the number of bytes of message data that can be inserted by or in the data portion of any streams message on the sys-
       tem.  If the tunable is set to zero, there is no limit on how many bytes can be placed in the data segment of the message.

       returns if the buffer being sent is larger than the current value of segments the data into multiple messages.

   Who Is Expected to Change This Tunable?
       Any customer.

   Restrictions on Changing
       Changes to this tunable take effect at next reboot.

   When Should the Value of This Tunable Be Raised?
       The tunable should be increased by any customer if the customer's STREAMS module/driver(s) require a longer message size in the	data  por-
       tion than the current value.

   What Are the Side Effects of Raising the Value of This Tunable?
       The kernel will use more memory.  During low memory situations, it may bring down system performance due to frequent swapping.

   When Should the Value of This Tunable Be Lowered?
       The  tunable  could  be lowered by any customer if the customer's STREAMS module/driver(s) do not require a longer message size in the data
       portion than the current value.

   What Are the Side Effects of Lowering the Value of This Tunable?
       Possible improper functioning in any of the STREAMS module/driver(s).  Possible performance degradation, particularly in networking.

   What Other Tunable Should Be Changed at the Same Time as This One?
       None.

WARNINGS

       All HP-UX kernel tunable parameters are release specific.  This parameter may be removed or have its meaning changed in future releases	of
       HP-UX.

       Installation  of  optional  kernel  software, from HP or other vendors, may cause changes to tunable parameter values.  After installation,
       some tunable parameters may no longer be at the default or recommended values.  For information about the effects of installation  on  tun-
       able  values,  consult  the documentation for the kernel software being installed.  For information about optional kernel software that was
       factory installed on your system, see at

AUTHOR

       was developed by HP.

							     Tunable Kernel Parameters						       STRMSGSZ(5)
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