A Closer Look at the Server Node

We’ve arrived at the heart of the server node: the SoC. Calxeda licensed ARM IP and built its own SoC around it, dubbed the Calxeda EnergyCore ECX-1000 SoC. This version is produced by TSMC at 40nm and runs at 1.1GHz to 1.4GHz.

Let’s start with a familiar block on the SoC (black): the external I/O controller. The chip has a SATA 2.0 controller capable of 3Gb/s, a General Purpose Media Controller (GPMC) providing SD and eMMC access, a PCIe controller, and an Ethernet controller providing up to 10Gbit speeds. PCIe connectivity cannot be used in this system, but Calxeda can make custom designs of the "motherboard" to let customers attach PCIe cards if requested.

Another component we have to introduce before arriving at the actual processor is the EnergyCore Management Engine (ECME). This is an SoC in its own right, not unlike a BMC you’d find in conventional servers. The ECME, powered by a Cortex-M3, provides firmware management, sensor readouts and controls the processor. In true BMC fashion, it can be controlled via an IPMI command set, currently implemented in Calxeda’s own version of ipmitool. If you want to shell into a node, you can use the ECME's Serial-over-LAN feature, yet it does not provide any KVM-like environment; there simply is no (mouse-controlled) graphical interface.

The Processor Complex

Having four 32-bit Cortex-A9 cores, each with 32 KB instruction and 32 KB data L1 per-core caches, the processor block is somewhat similar to what we find inside modern smarphones. One difference is that this SoC contains a 4MB ECC enabled L2 cache, while most smartphone SoCs have a 1MB L2 cache.

These four Cortex-A9 cores operate between 1.1GHz and 1.4GHz, with NEON extensions for optimized SIMD processing, a dedicated FPU, and “TrustZone” technology, comparable to the NX/XD extension from x86 CPUs. The Cortex-A9 can decode two instructions per clock and dispatch up to four. This compares well with the Atom (2/2) but of course is nowhere near the current Xeon "Sandy Bridge" E5 (4/5 decode, 6 issue). But the real kicker for this SoC is its power usage, which Calxeda claims to be as low as 5W for the whole server node under load at 1.1GHz and only 0.5W when idling.

The Fabric

The last block in the Soc is the EC Fabric Switch. The EC Fabric switch is an 8X8 crossbar switch that links to five XAUI ports. These external links are used to connect to the rest of the fabric (adjacent server nodes and the SFPs) or to connect SATA 2 ports. The OS on top of server nodes sees two 10Gbit Ethernet interfaces.

As Calxeda advertises their offerings with scaling out as one of the major features, they have created fast and high volume links between each node. The fabric has a number of link topology options and specific optimizations to provide speed when needed or save power when the application does not need high bandwidth. For example, the links of the fabric can be set to operate at 1, 2.5, 5 and 10Gb/s.

A big plus for their approach is that you do not need expensive 10Gbit top-of-rack switches linking up each node; instead you just need to plug in a cable between two boxes making the fabric span across. Please note that this is not the same as in virtualized switches, where the CPU is busy handling the layer-2 traffic; the fabric switch is actually a physical, distributed layer-2 switch that operates completely autonomously—the CPU complex doesn’t need to be powered on for the switch to work.

It's a Cluster, Not a Server Software Support & The ARM Server CPU
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  • Kurge - Wednesday, March 13, 2013 - link

    Yeah, should have had two teams - each with goal to optimize on each platform. The Xeon team would not (lol) load up 24 VM's to serve the same web app. It's silly. Go bare metal in that use case.

    There will be different needs for different cases. The "lets load up a bunch of VMs" is useful to cloud providers and in other cases, but not for "I want to feed this app to as many users as possible".
  • dig23 - Tuesday, March 12, 2013 - link

    Interesting article and great first effort but felt bit outdated on both ATOM as well as ARM front, I am not blaming you, just saying.
  • JarredWalton - Tuesday, March 12, 2013 - link

    Outdated in what sense? No one else has really made a serious attempt to review thee Calxedas stuff, and while there are better Atom option out there, as Johan notes we were unable to get any in-house in time for testing. Or do you mean Calxedas' use of Cortex-A9 is outdated? If so, that's more of a case of laying the groundwork I think. Assuming they have their A15 option be backwards compatible with the current system (e.g. just get a new set of cards with the updated SoCs), that would be very cool.
  • JohanAnandtech - Wednesday, March 13, 2013 - link

    I can only agree with Jarred. There are no A15 server chips AFAIK, and unless I have missed a launch, I think the Atom N2800 is not outdated at all (Dec 2011).
  • aryonoco - Wednesday, March 13, 2013 - link

    This was a fabulous and most informative write up. You answered so many of my questions with this article. Excellent job covering an area that no one else is, and also kudos for running such great benchmarks.

    This really is tech journalism at its best. Thank you Johan, and thank you Anand for employing such high-quality writers.

    We all know how memory constrained the ARM A9 is. Even something like Krait would solve a lot of A9's traditional weak areas. And yet, it looks like the Calxeda makes sense in enough niches to be sustain their R&D and development efforts. Low-to-medium traffic web hosting, media streaming and storage. Each one of those areas is a sizeable market and the Calxeda solution offers enough to be seriously considered in these makets.

    And when one thinks about how many years of x86 optimisation has gone into the toolchain in things like the gcc, one realises the potential that lies ahead for ARM in this market. ARM's future roadmap is well known, next is Cortex A15 and then Cortex A57. Meanwhile there will be more software optimisation, and the management/deployment side will also improve. With all these in mind, I think it's more than conceivable that ARM will grab up to 20% marketshare in the server market by 2015.
  • JohanAnandtech - Wednesday, March 13, 2013 - link

    Thanks! Good summary... and indeed 20% marketshare is not impossible. The real questions is whether Intel give the Atom it is long overdue architecture update, or will Haswell put some pressure from above? Exciting times.
  • beginner99 - Wednesday, March 13, 2013 - link

    Isn't it much easier to administer 24 virtual servers than 24 physical ones (cost of personnel)? When all servers have the same workload it look sgood for ARM but the virtualized intel environment easily wins if some servers get a lot more requests than others, meaning too much for one ARM SOC to handle. The tested scenario is basically the best one could ever hope for the ARM server and pretty unrealistic (same load for all servers). That's fine but then also post worst-case scenarios...Intel server is a lot more flexible.
  • hardwaremister - Wednesday, March 13, 2013 - link

    I completely agree with the other readers that this writing is just absolutely superb. Fantastic novel job Johan.
    However, I also agree with the above commenter: a big part coup on virtualizing a "fat" core system is to be able to properly utilize the resources of the machine across VMs. By equally loading "tiny tiles", the obvious advantage of the inherent load balancing of a virtualized infrastructure completely disappears.
    Under current the current "fat" VM infrastructure you can accomodate individual VMs with heterogeneous loading levels, with extra provisioning in the resource pool.
    That is just not simply the case for these tests based on an army of individual machines against a many VMs virtualized under a few "fat" cpus.
    I don't mean to be overcritical, but this is a proper apples vs oranges comparison.
  • bobbozzo - Wednesday, March 13, 2013 - link

    A lot of shared hosting ISP's use lightweight virtualization with Linux or BSD "Containers". I would like to see you re-benchmark with those on both servers instead of using VMs.
    You should see higher performance vs full virtualization. I'm not sure how it would affect the ARM performance, but it shouldn't hurt much, and there is more potential for better load sharing if some sites are busier than others.
  • Jambe - Wednesday, March 13, 2013 - link

    Surprising, indeed! Thoroughgoing as usual, and excellently written.

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