Ghostwrite – Now This is Weird
Observations from Uppsala » Computer Architecture
by Jakob
3w ago
In August, a strange security vulnerability dubbed “Ghostwrite” was making the rounds in the press. Basically, a vector store instruction on an Alibaba T-Head C910 RISC-V-based processor would just write to a physical address without doing a virtual-to-physical translation or checking any kind of access rights. That is just totally weird. Just how could that ..read more
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The Event at the End of Universe
Observations from Uppsala » Computer Architecture
by Jakob
1M ago
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. Which Hardware? The CLINT interrupt controller used by many RISC-V designs has a built-in ..read more
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Useful Instruction Set Computing
Observations from Uppsala » Computer Architecture
by Jakob
3M ago
I tend to get into discussions about computer processor instruction-set architecture (ISA) design. ISA design is far from my day job, but it is an interesting topic where everyone working with computers at the machine level have opinions. Typically based on a mix of personal experience and fond memories of particular machines. This in turn ..read more
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Schloss Dagstuhl (and a Seminar and Cerebras)
Observations from Uppsala » Computer Architecture
by Jakob
4M ago
A month ago, I participated in a seminar at Schloss Dagstuhl in Germany, about “Discrete Algorithms on Modern and Emerging Compute Infrastructure”. Not my usual cup of tea, but it was very interesting and insightful nevertheless. I have attended a Dagstuhl seminar once before, back in 2003. Schloss Dagstuhl Dagstuhl is a very special institution ..read more
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“RISC-V in Practice” – Computer and System Architecture Unraveled Event Three
Observations from Uppsala » Computer Architecture
by Jakob
8M ago
On Wednesday, March 13, we had our third CaSA, Computer and System Architecture Unraveled, meetup. Same place as the previous, the 25th floor of the Kista Science Tower building, thanks to the kind sponsorship of Vasakronan and our collaboration with Kista Science City. The theme this time was “The RISC-V ISA in Practice”, with two ..read more
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“Packet Networks are not Socket Science” – Computer and System Architecture Unraveled Event Two
Observations from Uppsala » Computer Architecture
by Jakob
1y ago
On Wednesday, November 22, we had our second CaSA, Computer and System Architecture Unraveled, meetup. Same place in Kista as the last time, the 25th floor of the Kista Science Tower building, thanks to the kind sponsorship of Vasakronan and our collaboration with Kista Science City. This time, the theme was networking – but not ..read more
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The first Computer and System Architecture Unraveled Event in Kista – Great Speakers, Great Fun!
Observations from Uppsala » Computer Architecture
by Jakob
1y ago
This past Wednesday evening we had our first CaSA, Computer and System Architecture Unraveled, event. CaSA is a meetup in Kista (Sweden) for people interested in computer architecture, system architecture, and how software and hardware interact down towards the lower levels of the stack. The topic for the inaugural event was Core Count Explosion: A ..read more
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SystemC Evolution Fika: Parallel SystemC
Observations from Uppsala » Computer Architecture
by Jakob
1y ago
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. The Event The SystemC Evolution Fika co ..read more
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Some Notes on Temporal Decoupling (Reposted)
Observations from Uppsala » Computer Architecture
by Jakob
1y ago
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. Making a fast virtual platform Performance is critical for virtual platforms ..read more
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Don’t Look behind the Curtain! (Please)
Observations from Uppsala » Computer Architecture
by Jakob
1y ago
In a previous blog, I talked a bit about the hazards of coding to an implementation and not a specification, based on 1980s home computers. While the specifics and peculiarities of that case is hopefully confined to old hardware, the lessons are still worth contemplating. There is a modern variant of this phenomenon that is based on open-source software, and that I must admit to feeling a bit annoyed by. Fundamentally, the question is this: when figuring out how to use an API – should you look at the documentation or the implementation? Software APIs A software API is (as we all know) is an in ..read more
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