Wind River Blog: Testing Multicore Scaling with a Simics QSP

A few years ago, I built a demo on Simics that used a hacked Freescale MPC8641D target that was forced to scale from 1 to 8 cores. Some interesting experiements could be made using this target, and it was nicely scalable for its time. However, I always wanted to have something just a bit bigger. Say 20 cores, or 100. Just to see what would happen. Finally, I got it.

The Simics QSP target that we quietly launched earlier this Summer is such a scalable target. As discussed in a blog post describing the architecture, it is designed to scale to 128 cores currently. Using this ability, I repeated my old experiments, but trying very large threads counts and target core counts. The results show clearly that the way that I coded my parallel computation program was pretty bad, and I really would like to try to rewrite it using some more modern threading library. All I need is time and a way to cross-compile Wool

Anyway, the new blog post is here.

Wind River Blog: Inside the Simics QSP – Additional Notes

There is a new post at my Wind River blog, about the design and technical contents of the new Simics Quick Start Platforms, more widely known as the QSP. The blog describes the virtual-only hardware that forms part of the QSP, and how it was designed. It is interesting to note that the hardware ended up a bit more complex that I initially thought it would be, since an ideal virtual platform should be very simple. Right? Turns out an OS complicates things.

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Youtube Movie on Reverse Execution (and a small bit of Reverse Debug)

We just uploaded a short movie about reverse execution and reverse debugging to Youtube, to the Wind River official channel. In the short time available in this demo, we really only show reverse execution. Reverse debug, as I define it, is not used much at all, as explaining what goes on when you start to put breakpoints into a program and analyze its behavior takes a surprising amount of time.

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Wind River Blog: Teaching Networking with Simics

On the Wind River corporate blog, I have put up a blog post about how Wind River Education Services is going to use Simics to teach networking. What is interesting with this approach is that it shows how a virtual platform can be used for tasks like teaching that don’t have much to do with hardware modeling or similar “typical” VP uses. In this case, the key value is encapsulation of a set of machines running real operating systems and software stacks, and with lots of networks connecting them.

Wind River Blog: Forcing Rare Bugs to Appear using Simics

There is a new post at my Wind River blog, about how a team of researchers at the University of Nebraska at Lincoln is using Simics to force rare bugs to manifest themselves as errors. They used Simics to control a target system to force it into rare situations much more likely to trigger latent bugs, requiring far fewer test runs compared to just randomly rerunning tests again and again and hoping to see a bug.

Wind River Blog: Crystal Forest on Simics

There is a new post at my Wind River blog, about Simics running a model of the new Intel Crystal Forest platform. Crystal Forest is a very complex piece of hardware, but I am pretty happy that we managed to demo it in an understandable way – by essentially using it as a black box and putting a pretty display on top of that (using Eclipse).

 

Wind River Blog: Fault Injection with Simics

There is a new post at my Wind River blog, about how you actually do fault injection in Simics. This particular post is pretty detailed, showing the actual architecture of a fault injector in Simics, not just “yes you can do it”. It includes actual diagrams of system components and how you can insert fault injection into an existing system, so it is a bit more technical than most my Wind River blog posts that tend to be more conceptual.

Reverse History Part Three – Products

In this final part of my series on the history of reverse debugging I will look at the products that launched around the mid-2000s and that finally made reverse debugging available in a commercially packaged product and not just research prototypes. Part one of this series provided a background on the technology and part two discussed various research papers on the topic going back to the early 1970s. The first commercial product featuring reverse debugging was launched in 2003, and then there have been a steady trickle of new products up until today.

Originally published in January 2012. Post updated 2012-09-28 with a revised timeline for Lauterbach CTS. Post updated 2016-04-05 to include Mozilla RR. Post updated 2016-12-26 to add Simulics. Post updated 2017-10-08 to add Microsoft WinDbg. Post updated 2018-07-28 to add Borland Turbo Debugger.

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EETimes Articles on Simics

I just had two articles published the Embedded Design part of the EETimes.

First, “Rethink your project planning with a virtual platform“, which talks about how virtual platforms can change your entire project planning. Essentially, by reducing project friction and risks related to hardware availability, software integration, and show-stopper bugs, you can make projects work much better.

Then we have “Transporting bugs with virtual checkpoints“, which is a shorter, popular science, version of the paper I published last year at S4D. This describes how you can use checkpointing in a virtual platform to communicate bugs across time, space, and teams.

Wind River Blog: How to Get Virtual

There is a new post at my Wind River blog, about how you build virtual platforms with Simics. The post is more about the methodology than the nature of models, cycle accuracy, endianness, and all the other details of virtual platform modeling. I have written about modeling methodology on this blog too, and in particular I would recommend looking at “Two perspectives on modeling“.

Wind River Blog: VxWorks 64-bit using Simics

There is a new post at my Wind River blog, about how Simics was used to kick-start the development of the 64-bit version of VxWorks. It is an interesting example of how to use a virtual platform as a model of something much simpler and gentler than actual hardware systems.

Wind River Blog: “IMA on Simics”

I have a fairly lengthy new blog post at my Wind River blog. This time, I interview Tennessee Carmel-Veilleux, a Canadian MSc student who have done some very smart things with Simics. His research is in IMA, Integrated Modular Avionics, and how to make that work on multicore.

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Wind River Blog: Virtual vs Physical Systems

I have a post at my Wind River blog, about the difference between virtual and physical systems. The key idea is this:

Comparing virtual and physical systems is like comparing apples and apples, not apples and oranges: while apples are mostly interchangeable, they is certainly variation between them. Some apples are best for eating, some are better for making sauce, some are pie material, and some are best for fermenting cider. The type you select depends on what you want to cook. The difference between physical and virtual hardware is similar: they can be used as replacements for each other to some extent, but the connoisseur can make much better use of both by looking at the differences.

Go there now and read i!

Additional Notes on Transporting Bugs with Checkpoints

This post features some additional notes on the topic of transporting bugs with checkpoints, which is the subject of a paper at the S4D 2010 conference.

The idea of transporting bugs with checkpoints is some ways obvious. If you have a checkpoint of a state, of course you move it. Right? However, changing how you think about reporting bugs takes time. There are also some practical issues to be resolved. The S4D paper goes into some of the aspects of making checkpointing practical.

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Multicore is not That Bad

I recently read a couple of articles on multicore that felt a bit like jumping back in time. In IEEE Spectrum, David Patterson at Berkeley’s parallel computing lab brings up the issue of just how hard it is to program in parallel and that this makes the wholesale move to multicore into something like a “hail Mary pass” for the computer industry. In Computer World, Chris Nicols at NICTA in Australia asks what you will do with a hundred cores – implying that there is not much you can do today. While both articles make some good points, I also think they should be taken with a grain of salt. Things are better than they make them seem. Continue reading “Multicore is not That Bad”

Wind River Blog: True Concurrency is Different

I have another blog up at Wind River. This one is about multicore bugs that cannot happen on multithreaded systems, and is called True Concurrency is Truly Different (Again). It bounces from a recent interesting Windows security flaw into how Simics works with multicore systems.

First Blog at Wind River!

One of the many nice effects of the Wind River acquisition of Simics is that I will be blogging as part of the Wind River Blog network. My first post there is up now, and it is a short (at least compared to a textbook, I admit it looks terribly long for a blog post) overview of how Simics works inside.

I think it is important for users of technologically advanced tools to know a bit of how they work. A classic example of this is compilers, where I taught an ESC class almost a decade ago which is my most popular piece of writing to date

CoWare SystemC Checkpointing

gearsContinuing on my series of posts about checkpointing in virtual platforms (see previous posts Simics, Cadence, our FDL paper), I have finally found a decent description of how CoWare does things for SystemC. It is pretty much the same approach as that taken by Cadence, in that it uses full stores a complete process state to disk, and uses special callbacks to handle the connection to open files and similar local resources on a system. The approach is described in a paper called  “A Checkpoint/Restore Framework for SystemC-Based Virtual Platforms”, by Stefan Kraemer and Reiner Leupers of RWTH Aachen, and Dietmar Petras, and Thomas Philipp of CoWare, published at the International Symposium on System-on-Chip, in Tampere, Finland, in October of 2009.

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Finally, a Bug!

butterflyPart of my daily work at Virtutech is building demos. One particularly interesting and frustrating aspect of demo-building is getting good raw material. I might have an idea like “let’s show how we unravel a randomly occurring hard-to-reproduce bug using Simics“. This then turns into a hard hunt for a program with a suitable bug in it… not the Simics tooling to resolve the bug. For some reason, when I best need bugs, I have hard time getting them into my code.

I guess it is Murphy’s law — if you really set out to want a bug to show up in your code, your code will stubbornly be perfect and refuse to break. If you set out to build a perfect piece of software, it will never work…

So I was actually quite happy a few weeks ago when I started to get random freezes in a test program I wrote to show multicore scaling. It was the perfect bug! It broke some demos that I wanted to have working, but fixing the code to make the other demos work was a very instructive lesson in multicore debug that would make for a nice demo in its own right. In the end, it managed to nicely illustrate some common wisdom about multicore software. It was not a trivial problem, fortunately.

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Freescale P4080, in Physical Form

freescale-logo-iconPast Tuesday, I attended the Freescale Design With Freescale (DWF) one-day technology event in Kista, Stockholm. This is a small-scale version of the big Freescale Technology Forum, and featured four tracks of talks running from the morning into the afternoon. All very technical, aimed at designing engineers.

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SiCS Multicore Day 2009

Last Friday, I attended this year’s edition of the SiCS Multicore Day. It was smaller in scale than last year, being only a single day rather than two days. The program was very high quality nevertheless, with keynote talks from Hazim Shafi of Microsoft, Richard Kaufmann of HP, and Anders Landin of Sun. Additionally, there was a mid-day three-track session with research and industry talks from the Swedish multicore community. Continue reading “SiCS Multicore Day 2009”

Checkpointing in SystemC @ FDL

fdllogosmallAlong with Marius Monton and Mark Burton of GreenSocs, I will be presenting a paper on checkpointing and SystemC at the FDL, Forum on Specification and Design Languages, in late September 2009.

The paper will explain how we did Simics-style checkpointing in SystemC, using the GreenSocs GreenConfig mechanisms to obtain an approximation for the Simics attribute system.

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The TLM DAC

46daclogoThe past few days here at DAC, a big theme has been transaction level modeling (TLM).

TLM is often considered to be SystemC TLM-2.0. Most of the statements from the EDA companies are to the effect that SystemC TLM-2.0 solves the problem of combining models from different sources. Scratching the surface of this happy picture, it is clear that it is not that simple…

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Cadence SystemC Checkpointing

gears1I while ago I wrote a blog post on checkpointing in virtual platforms, and what it is good for. Checkpointing has been a fairly rare feature in virtual platform tools for some reason, but it seems to be picking up some implementations. In particular, I recently noticed that Cadence added it to their simulator solutions a while ago (2007 according to their blog posts). There are a two blog posts  by George Frazier of Cadence (“saving boot time” and “advanced usage“) that offer some insight into what is going on.

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