Understanding RT by graphics

A lot of people seem not to understand very well what real-time means. They usually tend to think RT has anything to do with performance and the raw throughput. It doesn’t. It’s all about determinism and guarantees.

This post’s title has “by graphics” words. I think the graphics below are worth a thousand words. I obtained them while porting the RT tree to Freescale boards some weeks ago at ProFUSION. Basically I’m running a task that wakes up every 40ms, run a tiny job, send some numbers through the network and sleeps again. The time in the graphics is the difference between the total time (sleep + wake-up + execution) and 40ms.

One important fact: while this is running, I’m running some CPU-intensive jobs in background and the board is receiving a ping flood from another host.

See that when the task is running with real-time priority, it doesn’t matter there’s a hugger job in background or someone is trying to take your board down with a ping flood. It’s always possible to draw a line and say it will never* go beyond that limit. In the other hand, when running with normal priority, the total time varies much more.

Task running with normal priority

Task running with real-time priority

PS.: In the graphics above I’m using an oscilloscope made by Arnaldo Carvalho de Melo. Thanks, acme.

* Well, never is a strong word. You better test with several scenarios, workloads, etc before saying that.

WebKit

After some time working with the EFL port of WebKit, I’ve been nominated as an official webkit developer. Now I have super powers in the official repository , but I swear I intend to use it with caution and responsibility. I’ll not forget Uncle Ben’s advice: ”with great power comes great responsibility”.

I’m preparing a post to talk about WebKit, EFL, eve (a new web browser based on WebKit + EFL) and how to easily embed a browser in your application. Stay tuned.

Now, officially an EFL developer

Last week I was officially added to EFL developers list. After contributing some patches to eina, edbus, elementary and E17 (especially to connman module), Gustavo Barbieri, who is also my boss at ProFUSION, added me to developers list giving me commit rights on EFL svn.

He said me some weeks ago that the only thing missing to add me as developer was that I’d have to use E as my window manager. Fair enough. If one wants to be a developer of a certain program, it’s better to first be an active user. So, last Friday I wiped out my Gnome and started using E17 as my default window manager. If you don’t know E, you should check its site. It’s a lightweight Desktop Environment designed on top of EFL, the Enlightnement Foundation Libraries.

I don’t think the current theme is that good, but I’m getting used to it. Hopefully, it will be replaced some time soon. Below, my current desktop with an animated wallpaper with a clock:

Enlightenment

Embedded Linux Conference 2010

So, today was the last day of the Embedded Linux Conference. Now, I’ll be here in USA for the Linux Collaboration Summit. It was really cool and it was amazing to meet people you are only used to chat, exchange some emails or that you heard about. Just to name some: Steven Rostedt, Greg Kroah-Hartman, Frank Rowand, Mike Anderson, Andrew Morton, Jon Corbet and others. I was really impressed too seeing Rostedt programming or Greg answering emails. What a great guys

And yesterday I presented my work, talking about the optimization of the Linux scheduler for soft real-time when running on multi-core architectures. I must admit I was a bit nervous, but it seems that people liked it. Following some pictures: