Mark Hermeling

Embedded Virtualization Opens New Possibilities

One of the things that stands out in many customer visits that I do is that embedded virtualization often enables possibilities that the customer never thought possible. This of course is a good thing, it may enable them to put a new product to market that the customer had never thought of. In a few cases I have seen customers use virtualization to shift their business models from shipping custom hardware to shipping software only using COTS boards. Virtualization in this case is used to provide the customization that they formerly needed hardware for.

Embedded Virtualization and Multi-Core

 VDC has released another report showing that multi-core is making fast inroads in embedded systems and we are seeing that at Wind River as well. There are exciting new possibilities with these chips, we have never had this much processing power in such small packages.

Consolidate, Consolidate, Consolidate

Many telecom applications are actually built up from multiple smaller sub-applications, often running on their own server in a rack, ATCA or otherwise. These servers run on multi-core processors, depending on the age of the last refresh this could be a dual, quad core or more. This is of course nothing new, what's new is how virtualization can improve server utilization.

Primary Virtualization Use Case

This topic invariably comes up when talking to customers, unfortunately, there is not just one, but several primary use cases. There are multiple ways to look into the various use cases. The one I like best is to look at generic drivers. An alternative is to look at actual usages in the various industries.

Hypervisors in Mobile

I received a bunch of emails today pointing to this blog from Jason Perlow. Jason has an interesting thought with regards to the Apple and HTC lawsuit that is brewing. Let me first say that I understand that companies have to protect their IP and that there are clearly important and enforceable patents out there, say Coca Cola's formula for well, Coca Cola. Apple certainly has a lot of valuable IP as well and they are spending a lot of dollars in making the user experience better. Some of these patents are vague at best, so I have mixed feelings on this and since I am not a lawyer I am going to leave it at that.

A sea of cores, now what?

A great number of cores gives more processing power, but this power needs to be harnessed. The easiest way to control a sea of cores is of course to run a single operating system over this sea in a Symmetric MultiProcessing mode (SMP). Most modern operating systems support this (which includes Wind River Linux and VxWorks of course).

The trick is to minimize the impact of Amdahl's law. This law describes the maximum theoretically attainable speedup on your multicore processor. Given a N core multicore processor, one would expect an application to run N times as fast, at least ideally.

The Beauty Of Partitioning

Developing for multicore often asks for new approaches to architecting embedded systems. A low-core-count multicore processor, say a 2 or 4 core processor, could be configured to use a single operating system in a SMP configuration. This would give one single OS control over both cores and is often a valid configuation. The OS should have features such as core affinity and core reservation. The former will lock a process to a core, but will allow other processes to use the core as well, the latter reserves a core for the exclusive use of a single process.

2010 Is The Year Of Embedded Virtualization

I believe that 2010 will be the year of embedded virtualization, all the signs point in the right direction. It always takes a while for new technology to grab the imagination of embedded device developers. Embedded developers are traditionally a conservative bunch, however, the benefits of virtualization can not be ignored, even by them.

Article: Multi-Core Slow Down

An interesting article by Dan Woods on Multi-core slowdown. The article tries to temper people's expectations with regards to multicore. The basic argument goes: A multicore processor has more raw processing power, but it requires the software load that runs on top of that processor to be able to use those cores, if not, the software could run at the same speed as single-core, or even slower.

One of the ways to use all the cores of course is multi-threaded programming in combination with an SMP operating system that can schedule over all the cores (SMP being Symmetric Multi Processing). Typically multi-threaded programs use multiple threads of execution and use synchronization primitives to make sure executions happens in the right order. The last thing you want is 2 threads 'simultaneously' modifying the same data structure. The thing is, one a single core processor, there is no true parallelism, the operating is pretending to do multiple things at once. When you introduce multicore processors you will have true parallelism, this may lead to problems.

One problem occurs when the application uses a lot of synchronization and the result is that the cores are continuously waiting on each other. You are now executing a largely serial application on a multicore part and Amdahl's law will dictate that you will have very little speed-up from the use of multiple cores.

Another possible problem is that your application does not use sufficient synchronization and the result is that the application will do things truly in parallel that were never meant to be executed in parallel. This often leads to data corruption and hard-to-find faults. Not a desirable situation either.

The statements in the article have more of an IT focus, however, they hold for embedded as well. Multicore could lead to a slow-down if the application is unable to use all this new processing power. However, in most cases there is a way to use the multiple cores and to make a difference, either in performance, or in the set of capabilities of a device.

One of the important points to consider when looking at multicore in embedded are the multicore software configuration. The most simple of these multicore configurations uses SMP which allows a single application to use multiple cores, if that application is written for it, as mentioned before. This seems to be the main focus of the original article.

However, other configurations allow customers to run multiple different operating systems on top of these multicore processors. There operating systems could be of the same type (say, VxWorks), or other types (say VxWorks and Linux). Each operating system runs in isolation and will use some of the raw processing power of that processor. Every operating system can of course run one or more applications.

Now, you may ask, why do I need to run multiple operating systems, can I not run multiple applications in a single SMP operating system? Yes you can, however, there are many situations where a single SMP OS is not the best solution because of safety, security, separation, robustness, performance or scalability reasons. Running multiple operating systems gives you, the user, better control as to how to use the power of your multicore processor.

One straight forward example of the use of multiple operating systems is that it allows a customer to use some of the cores in a multicore processor to add more functionality to an existing product using a different operating systems. For example, graphics capabilities using Linux added to the real-time control for an industrial application, or networking to a consumer device. This capability can provide benefits in many different industries, for example consumer applications, network switches, industrial applications, aero-space and defense, the examples are many.

Running more operating systems provides more flexibility such that you can provide more features or more performance to your customers and through that deliver a more competitive, higher value product.

Breadth and flexibility here are important. There is no silver bullet. SMP, uAMP, sAMP, virtualization, all are configurations in the tool-box of the embedded developer and can be used in many different combinations and situations.

There are a a couple of challenges that become immediately apparent:

• The first challenge is to use the right configuration at the right time (a screw driver does not work well if you need a hammer)
• The second challenge is to make sure that everything is integrated, the operating systems have to be optimized for the virtualization layer as well as the silicon
• The last, but certainly not the least is that with these additional configurations, we still need tools for development, analyze, debug and test, that need has not gone away

To summarize: a slowdown when using multicore is certainly possible, but there are ways to solve that slowdown:

1. Make your make your application aware of the multiple cores
2. Using the multiple cores to do new things, possible with new operating system

Primary Multicore Software Configurations

Many people ask the question as to what the best approach would be for them to go to multicore and/or virtualization. This is a great question to start a discussion as there is not a single silver bullet. I meant to post a quick diagram on the different multicore configurations before, but life has been busy since we announced the Wind River Hypervisor earlier this year. Busy in this case is certainly a good thing.