I had many interesting conversations at the HiPEAC 2017 conference in Stockholm back in January 2017. One topic that came up several times was the GEM5 research simulator, and some cool tricks implemented in it in order to speed up the execution of computer architecture experiments. Later, I located some research papers explaining the “full speed ahead” technology in more detail. The mix of fast simulation using virtualization and clever tricks with cache warming is worth a blog post.
Doing continuous integration and continuous delivery for embedded systems is not necessarily all that easy. You need to get tools in place to support automatic testing, and free yourself from unneeded hardware dependencies. Based on an inspiring talk by Mike Long from Norway, I have a piece on how simulation helps with embedded CI and CD on my Software Evangelist blog on the Intel Developer Zone.
It is really sad that the European Space Agency (ESA) lost their Schiaparelli lander last year, as we will miss out on a lot of Mars science. From a software engineering and testing perspective, the story of why the landing failed rather instructive, though. It gets down to how software can be written and tested to deal with unexpected inputs in unexpected circumstances. I wrote a piece about this on my blog at the Intel Developer Zone.
A new entry just showed up in the world of reverse debugging – Simulics, from German company Simulics. It does seem like the company and the tool are called the same. Simulics is a rather rare breed, the full-system-simulation-based reverse debugger. We have actually only seen a few these in history, with Simics being the primary example. Most reverse debuggers apply to user-level code and use various forms of OS call intercepts to create a reproducible run. Since the Simulics company clearly comes from the deeply embedded systems field, it makes sense to take the full-system approach since that makes it possible to debug code such as interrupt handlers.
I have also updated my history of commercial reverse debuggers to include Simulics.
Simics and other simulation solutions are a great way to add more variation to your software testing. I have just documented a nice case of this on my blog at the Intel Developer Zone (IDZ), where the Simics team found a bug in how Xen deals with MPX instructions when using VT-x. Thanks to running on Simics, where scenarios not available in current hardware are easy to set up.
I am going to present a paper about our new SystemC Library in Simics, at the DVCon Europe conference taking place in München next month. The paper is titled “Integrating Different Types of Models into a Complete Virtual System – The Simics SystemC* Library”, and I authored it together with my Intel colleagues Andreas Hedström, Xiuliang Wang, and Håkan Zeffer.
On my Intel Software Evangelist blog, I just published an updated version of an interview I first published back in May, about how to use Intel CoFluent Studio for IoT system architecture. This is a really cool story, about how you can use a calibrated simulation model to architect and analyze software performance before actually writing the code! I
My first blog post as a software evangelist at Intel was published last week. In it, I tell the story of how our development teams used Simics to test the software behavior (UEFI, in particular) when a server is configured with several terabytes of RAM. Without having said server in physical form – just as a simulation. And running that simulation on a small host with just 256 GB of RAM. I.e., the host RAM is just a small fraction of the target. That’s the kind of things that you can do with Simics – the framework has a lot of smarts in it.
It was rather interesting to realize that just the OS page tables for this kind of system occupies gigabytes of RAM… but that just underscores just how gigantic six terabytes of memory really is.
This really happened last week, but I was in the US for the DAC then. I did another blog on Intel Software blog, about a white paper that Wind River put out about how they use Simics internally. The white paper is a really good set of examples of how Simics can be used for software development, test, and debug – regardless of how old or new the hardware is. It also touches my favorite topic of IoT simulation and scaling up – Wind River is actually using Simics for 1000+ node tests of IoT software! Read on at https://blogs.intel.com/evangelists/2016/06/06/wind-river-uses-simics-test-massive-iot-networks/
I love bug and debug stories in general. Bugs are a fun and interesting part of software engineering, programming, and systems development. Stories that involve running Simics on Simics to find bugs are a particular category that is fascinating, as it shows how to apply serious software technology to solve problems related to said serious software technology. On the Intel Software and Services blog, I just posted a story about just that: debugging a Linux kernel bug provoked by Simics, by running Simics on a small network of machines inside of Simics. See https://blogs.intel.com/evangelists/2016/05/30/finding-kernel-1-2-3-bug-running-wind-river-simics-simics/ for the full story.
I have posted my first blog post to the Intel Software and Services blog channel. The Intel Software and Services blog is one channel in the Intel corporate blog you find at https://blogs.intel.com/. Other bloggers on the Software and Services channel write about security, UEFI, cloud, graphics, open source software, and other topics. Intel has a large software development community, and we produce quite a bit of software – and we do write about the innovations that come out of Intel that rely on software.
On my part, I will be posting more materials on simulation at Intel, as part of my role as a simulation evangelist on the Software and Service blog channel.
Even though I am now working for Intel, the nice folks at Wind River have let me do blogging on the Wind River blog as a guest anyway. I first blogged about the fantastic world of simulators that I have found inside Intel, and now a longer technical piece has appeared on a use of Intel CoFluent Studio. I interviewed Sangeeta Ghangam at Intel, who used CoFluent Studio to model the behavior of a complex software load on a gateway, connected to a set of sensor nodes. It is rather different from the very concrete software execution I work on with Simics. Being able to model and estimate the performance and cost and size of systems before you go to the concrete implementation is an important part of software and systems architecture, and CoFluent offers a neat tool for that.
Read the full story on the Wind River blog!
IEEE Micro published an article called “Architectural Simulators Considered Harmful”, by Nowatski et al, in the November-December 2015 issue. It is a harsh critique of how computer architecture research is performed today, and its uninformed overreliance on architectural simulators. I have to say I mostly agree with what they say. The article follows in a good tradition of articles from the University of Wisconsin-Madison of critiquing how computer architecture research is performed, and I definitely applaud this type of critique.
A long time ago, when I was a PhD student at Uppsala University, I supervised a few Master’s students at the company CC-Systems, in some topics related to the simulation of real-time distributed computer systems for the purpose of software testing. One of the students, Magnus Nilsson, worked on a concept called “Time-Accurate Simulation”, where we annotated the source code of a program with the time it would take to execute (roughly) on the its eventual hardware platform. It was a workable idea at the time that we used for the simulation of distributed CAN systems. So, I was surprised and intrigued when I saw the same idea pop up in a paper written last year – only taken to the next level (or two) and used for detailed hardware design!
Continue reading “Time-Accurate Simulation Revisited – 15 years later”
Intel is a big Simics user, but most of the time Intel internal use of Simics is kept internal. However, we recently had the chance to interview Karthik Kumar and Thomas Willhalm of Intel about how they used Simics to interact with external companies and improve Intel hardware designs. The interview is found on the Wind River blog network.
It is also my last blog post written at Wind River; since January 18, I am working at Intel. I am working on ways to keep publishing texts about Simics and simulation, but the details are not yet clear.
On November 3, 2015, I will give a presentation at the Embedded Conference Scandinavia about simulating IoT systems. The conference program can be found at http://www.svenskelektronik.se/ECS/ECS15/Program.html, with my session detailed at http://www.svenskelektronik.se/ECS/ECS15/Program/IoT%20Development.html.
My topic is how to realistically simulate very large IoT networks for software testing and system development. This is a fun field where I have spent significant time recently. Only a couple of weeks ago, I tried my hand simulating a 1000-node network. Which worked! I had 1000 ARM-based nodes running VxWorks running at the same time, inside a single Simics process, and at speeds close to real time! It did use some 55GB of RAM, which I think is a personal record for largest use of system resources from a single process. Still, it only took a dozen processors to do it.
There is a new post at my Wind River blog, about the new Wind River Helix Lab Cloud product that we launched for real last week. The Lab Cloud is a really cool way to expose Simics-style functionality, and my blog goes through some of the more prominent use cases for a simulator in the cloud. There a couple of demo videos linked from the blog, and I have also set up a Youtube playlist collecting the Simics demos and other videos that we have posted there. Quite a set over the past few years, actually!
There is a new post at my Wind River blog, about how I helped a colleague resolve a real problem using the preview version of the new Helix Lab Cloud system. The Lab Cloud right now is basically Simics behind a simplified web user interface, exposing the checkpointing and record-replay facilities in a very clear way. You can also share your sessions for live interactions with other people, which is truly cool.
While I was on vacation, Wind River published a blog post I wrote about the new multicore accelerator feature of Simics 5. The post has some details on what we did, and some of the things we learnt about simulation performance.
I have read a few news items and blog posts recently about how various types of software running on top of virtual machines and emulators have managed to either break the emulators or at least detect their presence and self-destruct. This is a fascinating topic, as it touches on the deep principles of computing: just because a piece of software can be Turing-equivalent to a piece of hardware does not mean that software that goes looking for the differences won’t find any or won’t be able to behave differently on a simulator and on the real thing.
There is a new post at my Wind River blog, about the Trinity of Simulation – the computer, the system, and the world. It discusses how you build a really complete system model using not just a virtual platform like Simics, but you also integrate it with a model of the system the computer sits in, as well as the world around it. Like this:
Read more about it in the blog post, and all the older blog posts it links to!
Last year, I concluded a programming project at work that clearly demonstrated that real programming tasks tend to involve multiple languages. I once made a remark to a journalist that there is a zoo of languages inside all real products, and my little project provided a very clear example of this. The project, as discussed previously, was to build an automated integration between a simple Simics target system and the Simulink processor-in-the-loop code testing system. In the course of this project, I used six or seven languages (depending on how you count), three C compilers, and three tools. Eight different compilers were involved in total.
There is a new post at my Wind River blog, about how Simics is used to simulate large wireless networks for IoT (Internet-of-Things) applications.
It is funny for me to be back at the IoT game. A decade ago (time flies, doesn’t it?), at Virtutech, I and Johan Runeson took part in an EU research project on exactly this topic. Unfortunately, we had to back out of that project due to economic circumstances and failing management commitment, but we still learnt a few things that were relevant now that we are back in the IoT game. In particular, how to simulate wireless networks in a reasonable way in a transaction-level simulator. Thus, payback for the investment took 10 years to arrive, but it did arrive. To me, that underscores the need to be a bit speculative, take some risk, and try to explore the future.
I am going to be speaking at the 2015 Embedded World Conference in Nürnberg, Germany. My talk is about Continuous Integration for embedded systems, and in particular how to enable it using simulation technology such as Simics.
My talk is at 16.00 to 16.30, in session 03/II, Software Quality I – Design & Verification Methods.
There is a new post at my Wind River blog, about how you can use Simics to enable the automatic testing of pretty much any computer system (as long as we can put it inside a simulator). This is a natural follow-up to the earlier post about continuous integration with Simics and Simics-Simulink integrations — automated test runs is a mandatory and necessary part of all modern software development.
At the Wind River corporate blog, there is a blog post that I wrote about continuous integration and Simics. At the Elsevier Computer Science Connect blog, there is also a blog post about continuous integration and Simics that I wrote. These two texts are essentially the same, and I had the good fortune to get it posted in multiple places. The reason it is up at Elsevier is to help promote our soon-to-be-released book at about virtual platforms and simulation (and a little bit about Simics), and hopefully we will reach a larger audience with both messages: CI with Simics is a great idea, and the book is a great book to buy.
During my vacation, a blog post went up on the Wind River blog with an interview with Hyungmin Cho, a researcher at Stanford. Hyungmin has done some seriously heavy and cool work with Simics, using it together with a circuit-level simulator to investigate error resiliency in hardware devices, and how errors propagate from hardware into the software. As part of this process, he has setup an automated test system using Simics, and this system has done more than a million automated Simics runs. That is an insane number – I have been using Simics for twelve years now, and if I had used it every day for all these years, I would have had to start 10 runs per hour, every hour of the day. It shows the power of automation along with parallel runs on clusters of machines – once the setup is automated, you can pour on the volume.
For the past six months I have not been doing much blogging at all, neither here nor on the Wind River blog. The reason is that I have been directing my writing energy into writing a text book about Simics together with Daniel Aarno at Intel. Last year, Daniel and I worked on an Intel Technology Journal issue on Simics. The ITJ issue was kind of a first step on the way to the book, collecting several articles about Simics usage at Intel and elsewhere. The book itself will be much more of a detailed description of Simics and how it works and why it works the way it works.
The September 2013 issue of the Intel Technology Journal (which actually arrived in December) is all about Simics. Daniel Aarno of Intel and I served as the content architects for the issue, which meant that we managed to contributed articles from various sources, and wrote an introductory article about Simics and its usage in general. It has taken a while to get this journal issue out, and now that it is done it feels just great! I am very happy about the quality of all the ten contributed articles, and reading the final versions of them actually taught me some new things you could do with Simics! I already wrote about the issue in a Wind River blog post, so in this my personal blog I want to be a little bit more, well, personal.
On the Wind River blog network, I have a short posting about network simulation with Simics. It points to the network demo video that we put up on Youtube a few weeks ago, along with some explanations of what is shown in the video. In short, we show a simple example of a network being simulated in Simics, along with some examples of what you can do with it.