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Wednesday 24 Dec 2008, 02:00pm
Multi-core - can you trust it?
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A couple of years ago, there was discussion about whether multi-core systems were really suitable for safety-critical systems. The answer? Yes they are.
Multiple processors usually make a system more reliable, more stable, and more suitable for use in circumstances where people will depend on it. If one fails, then others can continue, perhaps giving time to fix the broken one.
While multi-core is a multi-processor architecture, there are differences. Among the most obvious is the fact that the cores in a processor, of necessity, get their power and data from the same connections - so multi-core doesn't eliminate the single point of failure.
"What really interests me is the suitability of multi-core devices for safety-critical systems," said Paul Parkinson, a senior systems architect with Wind River in the UK. "The type of software platform which can be supported seems to be dependent on the level of flexibility of the multi-core architecture, and whether the cores can be configured to operate in an independent manner, or whether there is coupling and/or dependencies between the cores as there are obvious ramifications in a safety-critical environment."
The problem comes down to "fault propagation paths", said Maarten Koning, a senior principal technologist at Wind River. If one part of the system fails, it can cause others to go down, sometimes in complex ways - for instance if one processor makes a lot of unnecessary disk reads, it might appear to be carrying on with its own work - and yet be blocking another processor which relies on that disk for a steady stream of fresh data.
Do multi-core chips help or hinder this? "Multi-core processors are one opportunity to insert a barrier for fault propagation paths," said Koning. "Simply put applications on separate cores so that they can’t steal CPU from each other directly. Multi-core processors are like having time and space partition technology in hardware."
There are problems though: "With multiple operating systems on a multi-core processor or even in a single processor with multiple virtualised processors, the layers of software in our devices get thicker and even harder to fathom," says Koning.
Fast forward to the present - and companies are launching products that use multi-core for safety-critical systems, with the benefit that they can be used in COTS (commercial off the shelf systems) which government bodies prefer to buy, over highly customised special boxes.
Kontron's PENTXM2 uses LynxOS-178, which was fully tested in "a large European global positioning system programme". It has 1.67 GHz (low power) dual-core Xeons, along with a server class memory controller hub (MCH) and up to 4GB of RAM.
More importantly, the company is confident it can perform as it is supposed to. So it looks like that's another question answered.
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