/dev/zero

Aught to be a good title for a book on Xen, no?

Anyway, while discussing Xen with the COO (and it just occurred to me, really this project should be the CTO’s, not the COOs… odd how the COO does all this stuff…) he came to the conclusion that, like openVZ and Virtuozzo, Xen guest systems shared the kernel with the Host. That didn’t sound right to me, but I couldn’t disprove it with my Xen server, where every DomU had an empty /boot.

So I updated the kernel in Dom0, but didn’t reboot. I now have a newer kernel installed than the one it’s currently running.
I then tweaked the /etc/xen-tools/xen-tools.conf and built a new DomU, to use the new kernel. Everything went without a hitch. I now have a Dom0 running 2.6.18-4-xen-686, with a domU running 2.6.18-6-xen-686. So it would seem that while they all “share” a kernel in the sense that they share a single install on the hard drive (all pulling from the dom0 /boot directory), they aren’t sharing a single instance of the kernel in memory.

I then tried to get a working CentOS 5 domU running, but ran into some snags. That will be another post.

On the heels of my raving about Gentoo, I find that while from and administrative perspective I like it, from a user perspective? Not so much.

I have two workstations at work. One is a Celeron 1.7ish, 1.5GB of RAM, running Windows XP. The internal web sites we use tend toward lots of javascript, plus another application that sucks up resources. Thus Firefox, when viewing our ticket system, our order database system and our server locator / user database system was running very sluggish.

I managed to acquire a second desktop, a P4 1.8Ghz, 1GB RAM system, on which I intended to install Linux. When I got that far, I installed Gentoo, running Xfce4, as a learning exercise. Everything went beautifully. Once I got Firefox and Thunderbird installed, I moved all my work that that system, using the Windows box only for the non-web based application that only has a Windows client. And since the speakers are hooked up to that system, I left Pidgin there as well.
The performance of Firefox on the Linux box is barely a marginal improvement.

My personal laptop, however, a Centrino 1.6 with 512MB of RAM running Ubuntu 7.10 and Gnome, running all the same web sites is at least 3x more responsive.
I even made sure I had exactly the same addons installed on the two Linux systems. By all lights, the Gentoo box should be smoking the laptop.

It’s got a faster (model) processor.
It has a faster (clock rate) processor.
It has 2x the RAM.
It’s got an “optimized” OS installed.
It’s running the light-weight Xfce4 window manager, compared to Gnome’s (and all the other bells and whistles I’ve installed) bloat.
The only thing I can figure is there’s something about the default compile settings Gentoo uses when building Firefox.

I must remember to reboot the Gentoo box and check if Hyperthreading is turned off in the BIOS. I’m running an SMP kernel but only seeing one CPU. I also need to check if a P4 1.8 has HT support…

I’m quickly becoming a fan of Gentoo.
I don’t think it will be replacing Ubuntu on my laptop, but I’m finding that for a “source based” system, it’s very easy to use. It doesn’t install anything you don’t absolutely need until you specifically ask for it, but when you do, it’s pretty painless. You just have to put up with it taking a little longer than other distros to get installed, since it has to download the source, then compile it.