topic Re: Reduce the no of Cores in RHEL 5.2 in Operating System - Linux

Reduce the no of Cores in RHEL 5.2

prakasse — Wed, 25 Feb 2009 05:14:17 GMT

Hi Folks,

I am currently using DL580 with 4P/16C. Earlier i installed RHEL 4.7 and i was able to reduce the no of cores by modifying th grub file.
1) Verified the current number of cores running.
4) Modified /boot/grub/grub.conf to adjust the "maxcpus" value and set the "default" boot command as needed.
5) Rebooted the system.
6) Verified that the system was running the newly requested number of cores.

Now i installed RHEL 5.2 and followed the same steps for reducing the number of cores. But the same is not happening. Can anyone help.

Thanks in advance,
Senthil.

P.S: Am facing this critical issue and i assure that the right answer will get full 10 points.

Re: Reduce the no of Cores in RHEL 5.2

Steven E. Protter — Wed, 25 Feb 2009 08:29:31 GMT

Shalom,

Core files can be completely prevented from being written at all.

ulimit settings can do this.

ulimit -c 0

This can be done in /etc/profile or the individual .profile for users.

SEP

Re: Reduce the no of Cores in RHEL 5.2

Vitaly Karasik_1 — Wed, 25 Feb 2009 08:57:20 GMT

Weird!
Do you see "maxcpus" param into "/proc/cmdline" in your running system?

Re: Reduce the no of Cores in RHEL 5.2

prakasse — Wed, 25 Feb 2009 08:57:24 GMT

Hi SEP,

By core i meant the number of cpu and not the core files. DL580 has 16 core, 16 cpus and i need to tell RHEL to use only 12 cpu and disable the other 4 cpus's.

Thanks,
Senthil

Re: Reduce the no of Cores in RHEL 5.2

Steven E. Protter — Wed, 25 Feb 2009 14:30:51 GMT

Oh, sorry.

RHEL ES will not support more than a certain number of cores.

The AS release will.

Note also CentOS is based on AS and will for free and out of the box support all 16 cores.

I was a little tired when I read your question. Sorry I misunderstood.

SEP

Re: Reduce the no of Cores in RHEL 5.2

Steven McCoy — Wed, 25 Feb 2009 15:13:09 GMT

Hey guys,

I think he's wanting to limit the amount of cores/CPUs that Linux is recognizing/using. He has 16 cores/CPUs showing up now, but wants to limit the number Linux sees to 12.

Is this correct, prakasse?

Re: Reduce the no of Cores in RHEL 5.2

Vitaly Karasik_1 — Wed, 25 Feb 2009 16:04:48 GMT

yes, as far as I understand.

Re: Reduce the no of Cores in RHEL 5.2

Steven E. Protter — Wed, 25 Feb 2009 16:32:54 GMT

Shalom,

Now I finally understand.

What is the reason for limiting the OS to 12 Cores? License by CPU costs for oracle has driven others to this solution.

Fixing this issue may require a patch.

There may be a bugzilla on this function for 5.2

SEP

Re: Reduce the no of Cores in RHEL 5.2

prakasse — Wed, 25 Feb 2009 17:19:28 GMT

Thansk for the responses. "/proc/cmdline" did the trick for verification.

As mpstat gave wrong results in 5.2

Re: Reduce the no of Cores in RHEL 5.2

prakasse — Wed, 25 Feb 2009 17:20:07 GMT

Solution found