There is a new blog post on my Wind River blog, about the Landslide system from CMU. It is a pretty impressive Master’s Thesis project that used the control that Simics has over interrupts to systematically try different OS kernel thread interleavings to find concurrency bugs. The blog is an interview with Ben Blum, the student who did the work. Ben is now a PhD student, and I bet that he will continue to generate cool stuff in the future.
Tag Archives: Operating Systems
I am not in the computer security business really, but I find the topic very interesting. The recent wide coverage and analysis of the Flame malware has been fascinating to follow. It is incredibly scary to see a “well-resourced (probably Western) nation-state” develop this kind of spyware, following on the confirmation that Stuxnet was made in the US (and Israel).
In any case, regardless of the resources behind the creation of such malware, one wonders if it could not be a bit more contained with a different way to structure our operating systems. In particular, Flame’s use of microphones, webcams, bluetooth, and screenshots to spy on users should be containable. Basically, wouldn’t cell-phone style sandboxing and capabilities settings make sense for a desktop OS too?
Edited on 2009-Feb-01, to include the link to the illustrated guide that really helps you get there faster. Thanks Simon! Also, promoted to front page, original post was put up on 2008-Nov-09.
Thanks to Simon Kågströms post (and the even better second-generation with screenshots) about using Eclipse for the Linux kernel, I have a much nicer work environment now for my ongoing work in learning Linux device drivers on PowerPC, which has helped me work my way through several hard-to-figure-out system calls. Read More →
The best way to learn something is to try, fail, and then try again. That is how I just learned the basics of multiprocessor interrupt management. For an educational setup, I have been creating a purely virtual virtual platform from scratch. This setup contains a large number of processors with local memory, and then a global shared memory, as well as a means for the processors to interrupt each other in order to notify about the presence of a message or synchronize in general. Getting this really right turned out to be not so easy.
There are times when working with virtual hardware and not real hardware feels very liberating and efficient (not to mention safe). Bringing up, modifying, and extending operating systems is one obvious such case. Recently, I have been preparing an open-source-based demonstration and education systems based on embedded PowerPC machines, and teaching myself how to do Linux device drivers in the process. This really brought out the best in virtual platform use.
More from the SiCS multicore days 2008.
There were some interesting comments on how to define efficiency in a world of plentiful cores. The theme from my previous blog post called “Real-Time Control when Cores Become Free” came up several times during the talks, panels, and discussions. It seems that this year, everybody agreed that we are heading to 100s or 1000s of “self-respecting” cores on a single chip, and that with that kind of core count, it is not too important to keep them all busy at all times at any cost. As I stated earlier, cores and instructions are now free, while other aspects are limiting, turning the classic optimization imperatives of computing on its head. Operating systems will become more about space-sharing than time-sharing, and it might make sense to dedicate processing cores to the sole job of impersonating peripheral units or doing polling work. Operating systems can also be simplified when the job of time-sharing is taken away, even if communications and resource management might well bring in some new interesting issues.
So, what is efficiency in this kind of environment?
This might appear as a stretched analogy, but it struck as me as obvious when I tried playing the Lego Racers boardgame with my 3-year old this weekend. The game is ranked pretty low on Boardgamegeek, and deservedly so. The promise and premise is great: use Lego cars to race around a track and pick up new pieces to modify the powers of your car… sounds like great fun. Right? But it is not, and that’s where my analogy with the age of software comes in.
Being a bit of a computer history buff, I am often struck by how most key concepts and ideas in computer science and computer architecture were all invented in some form or the other before 1970. And commonly by IBM. This goes for caches, virtual memory, pipelining, out-of-order execution, virtual machines, operating systems, multitasking, byte-code machines, etc. Even so, I have found a quite extraordinary example of this that actually surprised me in its range of modern techniques employed. This is a follow-up to a previous post, after having actually digested the paper I talked about earlier.
It just dawned on me recently (and it sure must have been obvious to those working with configuring AMP — Assymtric Multiprocessing Systems) that in an AMP setup, the operating systems involved actually know about each other and have to account for the fact that they are sharing a single processor chip with other operating systems. So you cannot just take two single-core operating system images from an existing multiple-processor (local memory) solution and put them on a single chip and things just work. You do need to prepare the boot process and find a way to nicely share the common I/O devices, timers, accelerator engines and other resources on the chip. This is materially different from a virtualized setup.
A company called Fastscale Technologies has a product that is simple in concept and yet very powerful. Instead of using complete installs of heavy operating systems like Linux or Windows to run applications on virtual machines, they offer tools that provide minimal operating system configurations that are tailored to the needs of a particular application. Since only that application is going to be run on the virtual machine, this is sufficient. According to press reports, this means that you can run several times more virtual machines on a given host, compared to default OS installs. And boot an order of a magnitude faster.