A Peek Inside IBM’s Merchant Power8 Processors

February 2, 2015 Timothy Prickett Morgan

Big Blue may have sold off its IBM Microelectronics chip making division to GlobalFoundries, but it is still in control of the Power8 processor and it is still very much interested in creating and selling merchant versions of the Power8 processors that it has created for its own Power Systems server lineup. A new report released from chip industry watcher The Linley Group has taken a look at these merchant-class Power8 chips and how they fit into the systems market.

Someday, a machine that an IBM i customer buys could end up coming from a third-party vendor, not from IBM itself, so it bears watching how this for-sale variant of the Power chip is distinct from the ones that IBM designs for its own use. Moreover, it is interesting to see what tweaks and changes IBM is making at behest of this parties like Google, Tyan, and Wistron, who are making their own motherboards and systems based on these merchant versions of the Power8 chip under the auspices of the OpenPower Foundation. There are more than a dozen system makers who are working on OpenPower machines based on the merchant Power8 chips, who expect to start delivering machinery around the middle of the year, as The Four Hundred has previously reported.

The Linley Group’s Microprocessor Report from late December was focused on the merchant-class Power8 chips, and you can get a copy of it at this link. As we have been saying since the details of the Power8 processor were announced more than a year and a half ago, this particular design is aimed specifically at heavy-lifting datacenter workloads where high memory bandwidth, large caches, and a large number of threads per socket are needed to support those workloads most efficiently. In many cases, the Power8 processors have fewer cores than the equivalent Intel “Haswell” Xeon E5-2600 v3 processors, which debuted in September last year, but they make up the difference in high clock speeds and high overall thread counts. The next result is that the Power8 chip does about twice the work of a Power7+ chip and can, at least on CPU-level integer and floating point benchmarks, give the Xeon E5 and even the higher-end Xeon E7 processors from Intel a serious run for the money. Intel has the thermal advantages, but surprisingly, The Linley Group thinks that IBM has a price advantage on its processors.

You heard that right. At least for the merchant chips, IBM is charging less for a roughly equivalent server processor than Intel. At the moment, says The Linley Group, IBM has three different merchant-class Power8 processors available to outside system builders. The idea is to give a variety of core and thread counts, cache sizes, and memory capacities and bandwidths while keeping everything within a thermal envelope of 190 watts for the processor and an additional 20 watts for every external “Centaur” memory buffer/control chip that links external main memory to the Power8 chip. The Linley Group reckons that IBM is charging $850 for an eight-core Power8 chip running at 3.76 GHz with 64 MB of embedded DRAM L3 cache memory. (That pricing is based on 1,000-unit tray volume purchases, just as Intel quotes its prices.) You have to pay another $90 a pop for each Centaur memory buffer chip, which also includes the L4 cache memory that feeds high bandwidth into the Power8 processor. Each merchant Power8 chip has two or four of these Centaur chips. The ten-core Power8 runs at 3.43 GHz, has 80 MB of L3 cache, and costs $1,650 plus the Centaurs, while the 12-core Power8 runs at 3.13 GHz, has 96 MB of L3 cache, and costs $2,500 plus the Centaurs. One thing to note. The rough performance of the eight-core and 10-core chips, in terms of SPEC integer and floating point benchmarks, is about the same, and the 12-core chip doesn’t boost the performance all that much on these low-level tests. IBM is offering a mix of threads and cache and clocks to suit different real-world workloads where these distinctions will matter. (The Linley Group is using unaudited SPEC benchmark tests as the basis of its analysis, so take that as you will.)

There are a couple of other interesting things to note. While the merchant-class Power8 chips can handily beat both the Intel Xeon E5 and E7 processors in terms of raw memory bandwidth, they do not offer as much memory bandwidth or memory capacity as the Power8 chips that IBM is offering in its own Power Systems line. IBM’s own Power8 variant can deliver 410 GB/sec of peak memory bandwidth across eight of the Centaur chips feeding into a single Power8 socket, which is twice the peak 205 GB/sec of the merchant Power8 parts. The Xeon top-end E5-2699 v3 chip tops out at 68 GB/sec across its four internal memory controllers, and the Xeon E7, which has its own external memory buffer chips (but no L4 cache) can only deliver 85.3 GB/sec of peak memory bandwidth. The other interesting thing The Linley Group found out about the merchant Power8 chips is that they have half as many PCI-Express 3.0 lanes for attaching peripherals to the processor complex as the Power8 chips IBM made for itself and they also have curtailed SMP/NUMA processor clustering capabilities compared to IBM’s homegrown Power8 chips. None of that means that IBM’s own Power Systems customers will ever come close to hitting the limits of peripheral expansion or processor scalability.

IBM has been pretty clear that the OpenPower effort, and therefore its merchant Power8 chips, are focused on the Linux operating system and not its own IBM i and AIX platforms, but that could change. IBM could decide to resell third party machines initially aimed at Linux to customers who want IBM i or AIX, and in fact, I fully expect that to happen over the long haul.

The fun bit is that because Intel has such hegemony in the two-socket server market these days that it can command a very high premium for its Xeon E5 and E7 processors, and by doing so it has left room for IBM to come in and carve a niche for itself with the Power8.

“Even if OpenPower systems never break out of this niche, their high performance can support the high margins that sustain a profitable business,” writes analyst Tom Halfhill in the Power8 report. “And those margins should remain high as long as Intel keeps its prices and margins high. OpenPower can generate extra revenue that helps IBM defray the costs of designing new Power processors for its own systems and for OEMs. The cost of offering Power processors as merchant products is relatively small, and any incremental profit is good for IBM’s server business.”

What we really need at this point are some system-level comparisons that take a look at thermals, performance, and costs, not just at the raw feeds and speeds for the processors and memory complexes. I will start working on that now.

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