computer simulation technology – Observations from Uppsala

Reversing out of Reverse

The Intel Simics simulator version 7 removed a long-standing feature from the simulator framework. Reverse execution is no longer available. In its place, in-memory snapshots were introduced, which arguably offer most of the benefits at a lower implementation cost. What happened? I’ve been asked about the reasoning behind the chance on several occasions since I left Intel. I’d like to share my perspective on the decision, as it highlights the challenges of turning an idea into a robust, shippable feature.

Time to Do Something New

The time has come to do something new. I am leaving Intel (and the Intel Simics team) at the end of September (2024). After more than twenty years with the team and the product this is a big step into the unknown. But when Intel offered a “retirement” package as part of its current round of cost reduction measures, I felt that it was a golden opportunity to find something new to do.

The Event at the End of Universe

This is a short story from the world of virtual platforms. It is about how hard – or easy – it is to model a simple and well-defined hardware behavior that turns out to mercilessly expose the limitations of simulation kernels.

Intel Blog: Parallelizing a Virtual Platform Model

There are many ways to use threading and parallelization to improve the performance of virtual platforms. It is not always easy to successfully use parallelization – it very much depends on the nature of the workloads and model setup – but when it works it can really help. I recently published a long blog post at Intel, detailing an idealized example of threading for a device model that is shipping in the Simics training package.

Intel Blog: How to Boot Linux on Virtual Platform

Booting a software stack on a virtual platform is a necessary part of most software flows. It might seem simple, but in practice there are many different ways that it can happen.

In a recent Intel Blog post, I go through five ways to boot Linux on virtual platforms. Including the cases of doing it just like the hardware, but also how to “cheat” and directly boot from a kernel without first wrapping it in a disk image or similar.

DVCon Europe 2023 – 10th Anniversary Edition

The 2023 DVCon (Design and Verification) Europe conference took place on November 14 and 15, in the traditional location of the Holiday Inn Munich City Center. This was the 10^th time the conference took place, serving as an excuse for a great anniversary dinner. Also new was the addition of a research track to provide academics publishing at the conference with the academic credit their work deserves. This year had a large number of papers related to virtual platforms, so writing this report has taken me longer than usual. There was just so much to cover.

Intel Blog: How Simics Executes Instructions

I recently added a blog post to the Intel Software blog about how the Intel Simics Simulator executes target-software instructions. The blog post appeared just before DVCon Europe (last week) and I did not have time to put a reflector here earlier.

That’s Odd: How iCue and Windows 11 Ruin Simics Performance

While working on some screenshots for an upcoming blog, I noticed something that something was off with the performance of Simics on my Windows 11 laptop. The CPU load did not quite go as high as I am used to – typically, compute-intense run should get close to 100% processor load using a single host thread to execute the simulation. Instead, I got to no more than about 50%, which was decidedly odd. I also had a screenshot from a few days earlier that showed some 90% CPU load. Turns out the culprit was a combination of factors, including the Windows 11 scheduler and the Corsair iCUE software pack.

DVCon Europe 2022. Verification, System Simulation, and People!

The 2022 DVCon (Design and Verification) Europe conference was back in physical form at its usual venue at the Holiday Inn München. It was a great conference, and just like at the 2022 DAC people were very happy to be back in person.

Notes from our DVCon Europe 2022 Tutorial

I presented a tutorial about the “verification of virtual platforms models” at DVCon Europe last week. The tutorial was prepared by me and Ola Dahl at Ericsson, but Ola unfortunately could not attend and present his part – so I had to learn his slides and style and do my best to be an Ola stand-in (tall order, we really missed you there Ola!). The title maybe did not entirely describe the contents – it was more a discussion around how to think about correctness and in particular specifications vs implementations. The best part was the animated discussion that we got going in the room, including some new insights from the audience that really added to the presented content.

Updated: Included an important point on software correctness that I forgot in the first publication.

Elektroniktidningen Magazine Article about DML

The November 2022 on-paper magazine from Swedish electronics news site Elektroniktidningen features an article I wrote about the Device Modeling Language (DML). Among many other really good articles.

Update: The article is now available online in HTML format.

DAC 2022 – Back in Person, Chiplets, an Award, and Much More

The 59th Design Automation Conference (DAC) took place in San Francisco, July 10-14, 2022. As always, the DAC provided a great place to learn about what is going on in EDA. The DAC is really three events in one: there is an industry trade-show/exhibition, a research conference that is considered the premier in EDA, and an engineering track where practitioners present their work in a less formal setting.

I had two talks in the engineering track – one on the Intel device modeling language (which actually won the best presentation award in the embedded sub-track), and one on using simulation technology to build hardware software-first.

The DAC was almost overwhelming in the richness of people and companies, but this blog tries to summarize the most prominent observations.

Intel Blog: Catching a Tricky Bug by Running Simics on Simics

I recently published a long post on the Intel Community Blog, talking about how my colleague Evgeny solved a nicely complicated bug using Simics-on-Simics. The bug involved UEFI, an operating system, SMM, SMI, and virtualization. Just another day in the office (or more like a year, given how long it took to get this one resolved).

SystemC Evolution Fika: Parallel SystemC

The SystemC Evolution Fika on April 7 had threading/parallelism as its theme. There were four speakers who presented various angles on how to parallelize SystemC models. The presentations and following discussion provided a variety of perspectives on threading as it can be applied in virtual platforms and other computer architecture simulations. It was pretty clear that the presenters and audience had quite different ideas about just what the target domain looks like and the best way to introduce parallelism to SystemC. Here is my take on what was said.

Some Notes on Temporal Decoupling (Reposted)

This blog post was originally posted at Intel back in 2018, but it has since been retired from the Intel blog system. As it is of general interest (in my opinion), here is a reposting (with a few small updates here and there).

Temporal decoupling is a key technology in virtual platforms, and can speed up the execution of a system by several orders of magnitude. In my own experiments, I have seen it provide a speedup of more than 1000x. Here, I will dig a little deeper into temporal decoupling and its semantic effects.