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CentOS 5 kernel compiled with HZ=100...Yum repository posted: Jun 12, 2007 9:19 AM

Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
See these threads for background:

http://www.vmware.com/community/thread.jspa?threadID=58736
http://www.vmware.com/community/thread.jspa?threadID=60462

I have setup a Yum repository with a custom kernel compiled with HZ=100 for CentOS 5. This kernel improves performance when running multiple CentOS guests on a single VMware Server.

These kernels have only have minimal testing so be cautious using them. Due to build problems the kernel modules are _NOT_ signed.

You can find the repository here with CentOS 4 and 5 kernels:

http://vmware.xaox.net/centos/

Download VMware.repo into your /etc/yum.repos.d for easy access.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

1. Jul 3, 2007 5:30 PM in response to: Xaox
Click to view larstr's profile Virtuoso vExpert
larstr
2,410 posts since
Mar 11, 2004
Are you providing both smp and non-smp versions of this kernel?

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

2. Jul 3, 2007 6:06 PM in response to: larstr
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
Yes, I have built all the kernels that make sense. The only kernels that don't make sense are the Xen kernels.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

3. Jul 4, 2007 12:51 AM in response to: Xaox
Click to view larstr's profile Virtuoso vExpert
larstr
2,410 posts since
Mar 11, 2004
That makes sense.. The list don't specify which kernels are smp or not. Which one should I choose?

[code]
# yum list|grep kernel
kernel.i686 2.6.18-8.el5 installed
kernel.i686 2.6.18-8.1.6.el5 installed
kernel-headers.i386 2.6.18-8.1.6.el5 installed
fortune-kernelcookies.i386 1.0-37.2.el5.rf rpmforge
fortune-kernelnewbies.i386 1.0-37.2.el5.rf rpmforge
kernel-PAE.i686 2.6.18-8.1.6.el5 updates
kernel-PAE-debuginfo.i686 2.6.18-8.1.4.el5.cento vmware
kernel-PAE-devel.i686 2.6.18-8.1.6.el5 updates
kernel-debuginfo.i686 2.6.18-8.1.4.el5.cento vmware
kernel-debuginfo-common.i686 2.6.18-8.1.4.el5.cento vmware
kernel-devel.i686 2.6.18-8.1.6.el5 updates
kernel-doc.noarch 2.6.18-8.1.6.el5 updates
kernel-xen.i686 2.6.18-8.1.6.el5 updates
kernel-xen-devel.i686 2.6.18-8.1.6.el5 updates
yum-kernel-module.noarch 1.0.4-2.el5.centos extras
# uname -a
Linux centos5mal 2.6.18-8.1.6.el5 #1 SMP Thu Jun 14 17:46:09 EDT 2007 i686 athlon i386 GNU/Linux
#
[/code]

As you see I'm using both yours and the rpmforge repos.

Lars

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

4. Jul 4, 2007 6:37 AM in response to: larstr
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
Sorry about that, I forgot that in CentOS 5 there are no "SMP" kernels since they are all SMP kernels.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

5. Jul 17, 2007 1:49 PM in response to: Xaox
Click to view utropicmedia-karl's profile Novice
utropicmedia-…
12 posts since
Jun 11, 2007
to the OP -

We have been seeing issues with CentOS 5 (and 4.4) running as guests where every 30-40s the guest freezes for a few seconds. Do you think this setting would change this behavior?

The reason I ask is because I just noticed the clock is drifting badly on the guest, I suspect the total magnitude of the clock drift is the sum of all the freezes.


Thanks.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

6. Jul 18, 2007 5:31 AM in response to: utropicmedia-…
Click to view larstr's profile Virtuoso vExpert
larstr
2,410 posts since
Mar 11, 2004
It seems that there are issues with having an SMP kernel, even at 100Hz . Testing has shown that it's still not optimal for a VM, especially if you don't have a very recent cpu architecture.

Please look at this bug report I filed regarding this issue: http://bugs.centos.org/view.php?id=2189

Lars

Message was edited by:
larstr

update:
More testing revealed that there seems to be a failure atleast in the current xaox kernel-2.6.18-8.1.4.el5.centos.plus.VMware.i686 kernel, not making it's performance optimal. However, a properly built SMP kernel will have better results, and a uni processor kernel would be even better. See the link above for details.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

7. Jul 18, 2007 6:01 AM in response to: larstr
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
I was not aware of your bug report in the CentOS bug tracker, but a quick look at the kernel config that was used in the build (/boot/config-*) reveals that HZ was in fact set to 1000Hz for the build.

I'll take a look at it and see if I can figure out what went wrong with the build.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

8. Jul 20, 2007 12:04 PM in response to: larstr
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
I have a new build out with the new (2-6-18-8.1.8) build that really have HZ=100. Let me know if that works.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

9. Jul 23, 2007 12:47 PM in response to: Xaox
Click to view robbedoes's profile Enthusiast
robbedoes
30 posts since
Jul 22, 2007
Hi !

Here's a centos noob.

If I'm not mistaken, steks involved are:
cd /tmp
wget http://vmware.xaox.net/centos/5.0/i386/kernel-devel-2.6.18-8.1.8.el5.centos.plus.VMware.i686.rpm
wget http://vmware.xaox.net/centos/5.0/RPM-GPG-KEY
wget http://vmware.xaox.net/centos/5.0/VMware.repo

mv VMware.repo /etc/yum.repos.d/
rpm -ivh kernel-devel-2.6.18-8.1.8.el5.centos.plus.VMware.i686.rpm
reboot

But It feels like missing something, how to choose THIS kernel ?

TIA !

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

10. Jul 25, 2007 1:52 PM in response to: robbedoes
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
Here is the easy way to use the repository:

cd /etc/yum.repos.d
wget http://vmware.xaox.net/centos/5.0/VMware.repo
yum install kernel

You will be asked about downloading and installing the GPG key - you should answer "y" for "Yes".

After that you can get updates by just doing your normal "yum update".

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

11. Jul 26, 2007 12:43 PM in response to: Xaox
Click to view boydd's profile Champion User Moderators
boydd
5,707 posts since
Jun 15, 2004
I finally got around to trying your recompiled kernels. Works great! Time is much better and seems that performance is too. :-)

100 Hz did the trick - now it would be nice if VMware would upgrade their vHardware to take advantage of the 1000Hz kernel.

DB

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

12. Jul 26, 2007 1:05 PM in response to: boydd
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
I'm not sure that they (VMware) could do anything about the performance using 1000Hz kernels. The problem with the 1000Hz kernel is that the guest is asking for 1000 clock tick interrupts per second. This is not too bad when you are just running 1 machine, but when you start running multiple machines the system starts spending more and more time just doing context switches just to inject an interrupt. The time on the system starts getting funny when VMware starts injecting "catchup" interrupts and the Guest OS thinks that it missed an interrupt. At this point the guest starts adding clock ticks to compensate for interrupts it assumes that it missed.

Using the old default system clock speed of 100Hz decreases the number of needed context switches by an order of magnitude and has the added benefit of having a more consistent interrupt pattern.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

13. Sep 12, 2007 4:13 PM in response to: Xaox
Click to view McLennan-Forrester's profile Lurker
McLennan-Forr…
1 posts since
May 18, 2007
:) :) :) :) :) :) :) :)

Love your work everyone.

Now here's a pretty picture...

http://screenshots.ipspace.com/9.13.633252712628125000.png

Do you think this is related to the "Asterisk won't run under VMWare" school of thought? Centos being the predominant platform, etc.

Re: CentOS 5 kernel compiled with HZ=100...Yum repository

14. Sep 12, 2007 5:49 PM in response to: McLennan-Forr…
Click to view Xaox's profile Enthusiast
Xaox
73 posts since
Mar 10, 2006
Thanks!

Without some context on the screenshot, I can only guess that you installed the VMware kernels before 8:55AM and the CPU usage is down to almost nothing. If so that is what I saw and the reason I'm maintaining the VMware kernel builds.

I'm not sure what you mean as far as "Asterisk won't run under VMware". With and without the VMware kernels, I have been able to run Asterisk on CentOS on VMware; however, at times sound generated by Asterisk using festival can be choppy. In fact I'm currently running a copy of Trixbox as a VMware guest for my home phone system and it works pretty well.
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