I’m very happy to say that I was selected again to work on Google Summer of Code with X.Org Foundation. Daniel will be my mentor again. Thanks Google. Thanks X.Org!

In the last year we did a nice work separating the input event generation code of the X server into a different thread. We saw some performance improvement there specially because the implementation is not using signals anymore to wake up the server when some device emits an event. The reason why is that when a process is in the uninterruptible sleep (D state) signals are delayed and the mouse cursor lags.

I was thinking how we could make remotely X clients totally connective with the server when both are behind a NAT/firewall.

We can imagine one big motivation to do this: a scenario where someone using his thin and poor machine wants to use the resources of some “fat” machines which he simply doesn’t know where they are seated. Those fat machines could be arranged through a P2P network of “X11 pool of resources” and the list of machines displayed to the user select his desired one (e.g. with minor lag/load). Someone more capitalist than me could go further and imagine a provider selling X11 resources to mobile devices. Or just open your home machine’s web browser in any place of the world. Well, the field of applications would be huge.

Today, Paulo Zanoni help me to put in a shape the VgaArbiter wiki page. The primary intention of that page is to bring more developers in that project and some users++ who could also help testing. Feedback is very welcome. Here is the link.

After a long journey I come back in this… So I did a set of benchmarks to evaluate the VGA arbitration versus the RAC usage. My goal is to evaluate the performance difference of a multi-head/multi-card environment, i.e., an Xorg using the RAC to another using the arbitration.

The experiments consisted of two applications running at the same time in each Xorg server, one at each screen. This is interesting because it stress the semaphore task of the arbiter inside kernel, creating race conditions between the screens. The experiments were performed ten times and the average result was picked.

The Resource Access Control inside Xorg is the guy responsible to take care of the various resources of memory and to share them in a wise manner when two or more graphics devices are active (think multi-head). As an alternative from RAC we can rely on VGA arbiter. So me and Paulo Zanoni spent the last days implementing “the glue” of Xorg to use the arbiter code with this purpose.

So we finally have a working code to do the arbitration of the VGA legacy instructions. The code is separated in three pieces: vgaarb module [0], which is the arbiter itself inside Linux; the libvgaaccess [1], a set of user space functions to access the arbiter; and xf86VGAarbiter [2], the implementation of the library inside Xorg.

Basically we wrapped all the functions of the Xorg which deals with VGA (those wrapped by the RAC and few others) using the lock/unlock functions of the libvgaaccess. Really ugly.