Improving SliTaz Performance as a Virtual Machine Guest and Reducing Power Consumption

["rcx" <rcx@xxxxxxxxxxxxxxxx>]

Greetings,

 

For the context of this email, I am running VirtualBox 2.1.4 on a Windows XP host, with an idle "justX" SliTaz as the VirtualBox guest.

 

While running SliTaz as a guest in a virtual machine, CPU usage on my VM host is spiked, even when SliTaz is idle.  On my VirtualBox host, CPU usage for VirtualBox ranges around 90-99% (you exact percentage, though, may vary based on your processor speed and number of cores).  Based on some work I've done, the enabling CONFIG_NO_HZ in the kernel configuration appears to address this issue.  Below are some high-level performance comparisons--

 

slitaz-cooking-justX (February 28, 2009)

 * 90-99% CPU usage on the host while the guest is idle

 

slitaz-tickless (based on the "justX" flavor)

 * 5-15% CPU usage on the host while the guest is idle

 

In addition to improving VM performance, CONFIG_NO_HZ can also reduce power consumption and heat output on "real" hardware, as noted by Phoronix (see references at the end).

 

I have uploaded the ISO image used for this comparison to http://users.zoominternet.net/~rcx/slitaz-tickless.iso .  While booting this ISO, the message "Switched to NOHz mode on CPU#0" can be seen.  I have also been running this CONFIG_NO_HZ-enabled kernel on "real" hardware and have not yet observed any negative impacts.

 

Considering the large difference in performance, I think there would be benefit in enabling CONFIG_NO_HZ in the default SliTaz kernel.  Is this something that would be possible to incorporate?

 

 

Thank you,

Matthew

 

 

P.S. For those who might be interested, below is some additional information on CONFIG_NO_HZ.

 

The last couple paragraphs of this CNET article note the benefits of CONFIG_NO_HZ (tickless kernel).

 * http://news.cnet.com/Linux-coders-tackle-power-efficiency/2100-1007_3-6192865.html

 

A few highlights from that article, in which Arjan van de Ven (a longtime kernel programmer now working at Intel) was interviewed for part of the content, noted a few things about tickless kernels--
* "The tickless kernel provides another indirect benefit when it comes to power efficiency: It enables better use of virtualization"
* "Tickless kernels mean that the virtualization software that underlies all those operating systems isn't unduly taxed with needless interruptions."
* "'If you have a server running 50 virtualized guests, and each guest has a timer tick 1,000 times per second, that is 50 thousand ticks per second, without even doing any work yet,' van de Ven said. 'With tickless, you go from 1,000 to maybe 10, and suddenly it becomes manageable to do 50 guests.'"
* "Michael Larabel, editor of the Phoronix site that tests Linux hardware performance, found the tickless kernel can cut power consumption from 28 watts to 26 watts in IBM's Pentium M-based ThinkPad R52 running Fedora 7.  'A tickless kernel, in conjunction with (processor-based) power-saving technologies, can go a long way in extending the life of the battery and reducing the heat output,' Larabel said."

Another reference is http://lesswatts.org/ - "Saving Power with Linux"