Linux Kernel autotunes itself?

[Jcrawford]

From 2.6 does the Linux Kernel autotunes itself? - This was something i heard on a call from a senior Linux Member. Could someone clarify this statement although it would be better for that person to clarify as he made the statement. I wanted to know if there was some meaning to that statement.

Thanks

Joe.

[Steven E. Protter]

Shalom Joe,

You might want to define what auto tune means to you.

There are kernel parameters that can get set with ranges, which does permit the kernel to change the running value without systems administrator intervention.

Beyond that, I've had to manually tune most kernel paramters by updating them in /proc or using sysctl

sysctl -a

# displays all running parameters. Might be instructive to run this and look at the results.

SEP

[Jcrawford]

Shalom Steve

Thanks!  I did not know that sysctl -a is an intrusive command! Could you please clarify how it could be intrusive as it is just reporting (similar to kmtune or kctume in HP-UX). Also, when you mention about the range, what are you referring to, could you give an example please?

Best Regards

Joe.

[Steven E. Protter]

Shalom again. :smileyhappy:

sysctl -a is not really instrusive.

It merely displays all kernel parameters.

Examples:

syscl -a

fs.dir-notify-enable = 1
fs.leases-enable = 1
fs.overflowgid = 65534
fs.overflowuid = 65534
fs.dentry-state = 177408        166387  45      0       0       0
fs.nr_open = 1048576
fs.file-max = 331662
fs.file-nr = 2550       0       331662
fs.inode-state = 156672 378     0       0       0       0       0
fs.inode-nr = 156672    378
fs.binfmt_misc.status = enabled[root@mercury ~]#

cd /proc/sys/kernel

[root@mercury kernel]# cat shmmax
68719476736

Now I can do a one time only change on shmmax on the command line

echo 6871947673 > shmmax

That parameter is now changed.

To do a permenent change that survives boot, that is where we are like kctune/kmtune

From the man page

       -w     Use this option when you want to change a sysctl setting.

       /sbin/sysctl -w kernel.domainname="example.com"
sysctl -a | grep kernel.domainname

Reboot.

You will see survival.

-a just shows you where stuff is set. -w is the intrusvie one, but not really bad.

Almost every kernel parameter is dynamic on Red Hat Linux.

SEP