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.
I used a part of the money that I earned on the SoC 2007 to buy a laptop to me. My university friends found a good price of a MacBook and we went to the shop in a total of 6 people (!) to buy this laptop trying to get some discount. It cost R$ 3400 (about USD 1800), a very cheap value to the Brazil standards.
Fine. My MacBook arrived one week ago. The shiny laptop is cool, but the OS really not. I tried to accustom myself for at least one week with that OS and I failed. The reason why is better explained by these guys below:
