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

CPU Choices

For this article, the only current-generation Intel Broadwell-EP processors we had in the lab were the Xeon E5-2699 v4 and Xeon E5-2650 v4. Comparing the IBM POWER8 with the former was not fair: the Xeon costs almost 3 times ($4115) more than the midrange POWER8 chip ($1500). The latter was not an option either with a TDP of 90W. There are no Intel chips with 190W TDP, so we had to compromise.

The most comparable CPU that was available to us was the Xeon E5-2690 v3. It is a higher end midrange Intel SKU (135W TDP) that came out around the same time as the POWER8. If the 190W TDP POWER8 cannot beat this 135W TDP chip, IBM's micro architects have not done a very good job. Don't let the 2.6 GHz label fool you: this Haswell Xeon can boost to 3.1 GHz when all cores are active and to 3.5 GHz in a single thread situation. So it does have 2 cores extra and similar clockspeeds.

However we can't ignore the current-generation Broadwell-EP entirely. To get a better idea how the midrange POWER8 compares to the latest Xeons, we had to add another midrange Xeon E5 v4 SKU. So we only enabled 14 of the 22-cores of the Xeon E5-2699 v4. This gives us a chip that is somewhere between the Xeon E5-2660 v4 (14 cores at 2 GHz) and E5-2680 v4 (14 cores at 2.4 GHz). Well, at least on paper. The Xeon E5-2680 v4 runs most of the time at 2.9 GHz in heavily multi-threaded situations (+5 steps, all cores active), while our Xeon E5-2699 v4 with 14 cores runs at 2.8 GHz (+6 turbo steps). As the TDP of the latter is higher, the turbo clock will be used for a higher percentage of the time. Bottom line, our Xeon E5-2699 v4 with 14 cores is very similar to an E5-2680 v4 with a 145 W TDP. As the Xeon E5-2680 costs around $1745, it is in the right price range. From a price/performance point of perspective that is as fair as we can get it.

For those looking to get the best performance per watt: we'll save you some time and tell you that it does not get any better than the Xeon E5-2600 v4 series. Intel really went all the way to make sure that the Broadwell EP Xeon is a power sipper. And although the performance step is small, the Xeon E5-2600 v4 consumes much less than a similar Xeon E5 v3 SKU, let alone a CPU with a 190W TDP (+ 60-80W memory buffers).

Benchmark Configuration and Methodology

Our testing was conducted on Ubuntu Server 15.10 (kernel 4.2.0) with gcc compiler version 5.2.1. The reason why we did not update was that we only got everything working with that version.

Last but not least, we want to note how the performance graphs have been color-coded. Orange is for used for the review POWER8 CPU. The latest generation of the Intel Xeon (v4) gets dark blue, the previous one (v3) gets light blue. Older Xeon generations are colored with the default gray.

IBM S812LC (2U)

The IBM S812LC is based up on Tyan's "Habanero" platform. The board inside the IBM server is thus designed by Tyan.

Intel's Xeon E5 Server – S2600WT (2U Chassis)

All C-states are enabled in the BIOS.

SuperMicro 6027R-73DARF (2U Chassis)

All C-states are enabled in the BIOS.

Other Notes

Both servers are fed by a standard European 230V (16 Amps max.) power line. The room temperature is monitored and kept at 23°C by our Airwell CRACs.