GSoC summary #1 - July 29

The current implementation of X Window System relies in a signal scheme to manage the input event coming from hardware devices. This scheme frequently get blocked when lot of IO is occurring (for instance, when the process is swapping in/out). Get blocked means for instance a jumping cursor on the screen and in GUI is always desirable to prioritize the system responsiveness for end users. The human/computer interface should be smooth and this is the most user visible aspect of a system.

The current DRM kernel modesetting tree is already taking care to update the cursor registers and paint it to the screen. Very cool [0].

What I’ve done today is a shortcut between the kernel input layer and DRM to update the cursor directly on screen without the X server be notified always. Of course, a lot of issues raised up together. So let’s try to delegates the tasks again.

userspace app (X server):

I really don’t like to read large blog posts. Anyway…

What I did so far is a separated thread that takes care only the injection stage on the X server queue. Who is interested with the results, please read some past posts in my blog. It is currently in a very good shape (synced with post-mpx merge, all input devices are inside the thread and etc). The implementation looks like this: thread #1 deals with - injection of input events from devices thread #2 deals with - processing of input events to clients - requests from known clients (rendering things) - new client that tries to connect (pretty easy to do)

For my SoC project I need some mechanism to evaluate the improvement of the input thread inside X. So I wrote a simple kernel driver that emulates the mouse device moving and emitting bits of a simple pattern. I don’t know if something like this already exists or if there are other ways to do it, but the fact is that the solution I thought took me only few hours between the moment that I imagined, collected some ideas on the Web and implemented it.

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.