Assessing IBM's POWER8, Part 2: Server Applications on OpenPOWER

Closing Thoughts: Microarchitecture

Wrapping things up, let's first look at the POWER8 from a microarchitectural point of view. The midrange POWER8 is able to offer significantly higher performance than the best midrange contemporary Xeon "Haswell-EP" E5s. Even the performance per watt can be quite good, but only in the right conditions (high average CPU load, complex workloads).

IBM's engineers got their act together in 2014. That might seem like a trivial thing to say, but "Netburst", "Bulldozer" and "Cell" designs show that building a balanced architecture is not an easy task.

Considering POWER8 Scale Out Servers

The performance data and analysis is all very interesting, but at the end of the day, what if you are a server buyer? The POWER8 servers are definitely not for everyone. For many people, the superior performance per watt ratio of the Xeon E5-2600 v4 is more attractive. In most virtualized environments, the CPU load is relatively low, and saving lots of power at low loads (at least 100W per socket) will keep the TCO a lot lower.

An – admittedly smaller – part of the market does not care that much about electricity bills, but rather favors performance per dollar. And in that case, the S812LC model that can use cheaper DIMMs to reach the same capacity (32 DIMMs slots instead of 16-24) combined with the relatively cheap POWER8 CPU can make sense. It is important to note that our benchmarks are definitely not the showcases. According to IBM, MariaDB and Postgres have been more optimized for the POWER8 than MySQL. In those cases, IBM claims up to 40% better performance than the Xeon E5-2690 v4.

Those IBM benchmarks show of course the POWER8 in the best light, but we feel we should not dismiss them, just take them with grain of salt. If you read our very first article about OpenPOWER on Linux, you will notice we had trouble getting many workloads to even run. Once we got it working, performance was suboptimal. Now, less than a year later, most of the performance problems have either vanished (MySQL, Spark) or improved a lot (OpenJDK). The OpenPOWER Linux ecosystem gets better at a very fast pace.

IBM asks $13141 for the S822LC ("for Big Data") which includes two 10-core POWER8s, 256 GB DRAM, two 1 TB disks. A similarly configured DELL R730 with Xeon E5-2680 v4 costs around $12-13k, a similar HP DL380 costs around $15-17k. Though it is admittedly debatable how large the price advantage is as the actual street prices are hard to determine. HP and IBM tend to give bigger discounts, but those discounts get smaller for the most affordable servers.

So although IBM will not convert the masses as the price advantage is not that large, the new POWER8 servers are competitively priced. The bottom line: the IBM POWER8 LC servers can offer you better performance per dollar than a similar x86 server. But it's not a guarantee; as a server buyer you have to do your research and check whether your application is among the POWER8 optimized ones, and what kind of CPU load profile your application has. The Intel Xeons, by comparison, require less research, and are much more "general purpose".

Meanwhile the most expensive of the new server models, the S822LC HPC with six quad port NVLINKs and four Tesla P100s, is unique in the HPC market. Given a workload that has real and meaningful bus bandwidth needs, and it is very likely that any Xeon server with 4 GPUs will have a lot of trouble competing with it.

Overall the new POWER8 servers are not a broad full scale attack on Intel's Xeon. Rather they are a potent attempt to establish some strong beachheads in a number of niche but key markets (GPU accelerated HPC, Big Data).

And looking towards the future, it's worth considering that the POWER9 will offer a scale out version without the expensive and power hogging memory buffers. With that in the works, it's clear that IBM and the members of the OpenPOWER foundations are definitely on the right track to grab a larger part of the server market.