Calxeda's ARM server tested
by Johan De Gelas on March 12, 2013 7:14 PM EST- Posted in
- IT Computing
- Arm
- Xeon
- Boston
- Calxeda
- server
- Enterprise CPUs
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.
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tech4real - Thursday, March 14, 2013 - link
Calxeda quotes 6W for the whole SOC. We don't know how much is used for all these uncore stuff. It's possible A9 core only burns around 800mW. Still quite a gap to 1.25W.Wilco1 - Thursday, March 14, 2013 - link
Assuming the 800mW figure is accurate and the uncore power stays the same, then a node would go from 6W to 7.8W - ie. 30% more power for 100% more performance. Or they could voltage scale down to 1.5GHz and get 65% more performance for 5% more power. While a 28nm A15 uses more power in both scenarios, it is also much faster, so perf/Watt is significantly better.tech4real - Thursday, March 14, 2013 - link
1. I guess we have to wait to see if it's really 2X perf from a9 to a15 in real tests. I personally wouldn't bet on that just yet.2. mostly likely the uncore power will increase too. i don't think the larger memory bandwidth will come free.
Wilco1 - Thursday, March 14, 2013 - link
1. We already know A15 is 50-60% faster than A9 per clock (and often more, particularly floating point), so that gives ~2x gain from 1.4GHz to 1.8GHz.2. The uncore power will be scaling down with process while the higher bandwidth demand from A15 will increase DRAM power. Without detailed figures it's reasonable to assume these balance each other out.
tech4real - Thursday, March 14, 2013 - link
then let's wait to see anand benchmarks the future a15 system.also since the real microserver battle is between the future a15 system and 22nm atom system, I am eager to see how it plays out.
Th-z - Wednesday, March 13, 2013 - link
Very interesting article, thanks! This really piques another curiosity: how does latest IBM Power based server fair these days.Flunk - Wednesday, March 13, 2013 - link
It really doesn't sound like the price\performance is there. Also, lack of Windows support makes it useless for those of us who run ASP.NET websites (like the company I work for).It's still nice to see companies trying something different from the standard strategy. Maybe this is be better in a few generations and take the web server market by storm. If we see a Windows Server arm I could see considering it as an option.
skyroski - Wednesday, March 13, 2013 - link
I agree your testing suite's method is good and ok, so you were testing in consideration with hosting providers, fair enough.However on the topic of if you were serving a single site would a standard Xeon be better or ARM based ones? Which - is the case of consideration to FB/Twitter/Google/Baidu etc..., whom are as I have been led to believe by the media this past year, companies that ARM partners are trying to sell this piece of kit to. This test unfortunately cannot tell us.
A quick search on Google on performance impact of VMs yielded a thread in the VMware community forum by a vExpert/Moderator that mentioned expectation of 90% performance, and frankly, no matter how small you think the performance impact of a VM maybe, it is still using up CPU cycles to emulate hardware, that point will remain true no matter how efficient the hypervisor gets.
Secondly, coupled with the overhead of running 24 physical copies of the OS + Apache + DB on a box that would otherwise be running a single copy of the OS + Apache + DB is total overkill (on that topic)
It would be great if you can also test Xeon's req/sec if it ran a single instance so we can see it from a different perspective, as of now as I said, your test is skewered towards hosting providers whom might invest in Calxeda to provide VPS alternatives. But to them (and their client base), the benefit of a VPS is it's portability, which, 24 physical ARM nodes isn't going to provide, so I don't see them considering it as an alternative solution anyway.
skyroski - Wednesday, March 13, 2013 - link
I also want to ask if your Xeon test server's network adapter is capable of and was using Intel VT-c?JohanAnandtech - Thursday, March 14, 2013 - link
It was using VMDq/Netqueue (via VMXnet) but not SR-IOV/VT-c