In my series (well, I have one previous post about checkpointing) about misunderstood simulation technology items, the turn has come to the most difficult of all it seems: determinism. Determinism is often misunderstood as meaning “unchanging” or “constant” behavior of the simulation. People tend to assume that a deterministic simulation will not reveal errors due to nondeterministic behavior or races in the modeled system, which is a complete misunderstanding. Determinism is a necessary feature of any simulation system that wants to be really helpful to its users, not an evil that hides errors.
I just read the panel interview at the start of the latest issue (Number 4, 2008) of ACM Queue. Here, you have Bryan Cantrill of Sun (the man behind dTrace) bemoan the difficulty of testing faults. In particular:
Part of the reason I’m interested in virtualization is as a development methodology. It has not delivered on this, but one of the things that I ask is can I use virtualization to automate someone pulling the Ethernet cable out of the jack? I can get a lot closer to simulating it if you let me create a toy virtual machine than I can running on the live machine.
Well, this already exists. It is a common feature to any virtual platform that is not a datacenter-oriented runtime engine like VmWare, Xen, LPAR, and its ilk. Doing fault injection is a primary use case for virtual platforms, especially for larger servers and systems featuring redundancy and fault tolerance.
I have another short technical piece published about Multicore Debug at the EETimes (and their network of related publications, like Embedded.com). Pretty short piece, and they cut out some bits to make it fit their format. Nothing new to fans of virtual platforms for software development, basically we can use virtual platforms to reintroduce control over parallel and for all practical purposes chaotic hardware/software systems.
In the book “Programming Embedded Systems — with C and GNU Development Tools“, authors Michael Barr and Anthony Massa make some statements on simulation that I just have to disagree with on principle. Read on for what. Note that overall this is a good book, I am not claiming that it is not. The Amazon reviews are pretty good, and having a foreword by Jack Ganssle is always a sign of quality. But I just have to correct them on one little fact…
The TimeSys Embedded Linux Podcast (also called LinuxLink Radio) is a nice listen about embedded computing using Linux. Sometimes they are a bit too open-source centric, though, and ignore very good tools that live in the classic commercial world. One such example is the recent episode 20 on debugging tools, where they totally ignore modern high-powered hardware-based debugging.