The IBM POWER8 Review: Challenging the Intel Xeon
by Johan De Gelas on November 6, 2015 8:00 AM EST- Posted in
- IT Computing
- CPUs
- Enterprise
- Enterprise CPUs
- IBM
- POWER
- POWER8
Energy and Pricing
Unfortunately, accurately and fairly comparing energy consumption at the system level between the S822L and other systems wasn't something we were able to do, as there were quite a few differences in the hardware configuration. For example, the IBM S822L had two SAS controllers and we had no idea how power hungry that chip under the copper heatsink was. Still there is no doubt that the dual CPU system is by far the most important power consumer when the server system is under load. In case of the IBM system, the Centaur chips will take their fair share too, but those chips are not optional. So we can only get a very rough idea how the power consumption compares.
| Xeon E5 299 v3/POWER8 Comparison (System) | ||
| Feature | 2x Xeon E5-2699v3 | 2x IBM POWER8 3.4 10c IBM S822L |
| Idle | 110-120W | 360-380W |
|
Running NAMD (FP) |
540-560W |
700-740W |
| Running 7-zip (Integer) |
300-350W |
780-800W |
The Haswell core was engineered for mobile use, and there is no denying that Intel's engineers are masters at saving power at low load.
The mightly POWER8 is cooled by a huge heatsink
IBM's POWER8 has pretty advanced power management, as besides p-states, power gating cores and the associated L3-cache should be possible. However, it seems that these features were not enabled out-of-the box for some reason as idle power was quite high. To be fair, we spent much more time on getting our software ported and tuned than on finding the optimal power settings. In the limited time we had with the machine, producing some decent benchmarking numbers was our top priority.
Also, the Centaur chips consume about 16W per chip (Typical, 20W TDP) and as we had 8 of them inside our S822L, those chips could easily be responsible for consuming around 100W.
Interestingly, the IBM POWER8 consumes more energy processing integers than floating point numbers. Which is the exact opposite of the Xeon, which consumes vastly more when crunching AVX/FP code.
Pricing
Though the cost of buying a system might be only "a drop in the bucket" in the total TCO picture in traditional IT departements running expensive ERP applications, it is an important factor for almost everybody else who buys Xeon systems. It is important to note that the list prices of IBM on their website are too high. It is a bad habit of a typical tier-one OEM.
Thankfully we managed to get some "real street prices", which are between 30% (one server) and 50% (many) lower. To that end we compared the price of the S822L with a discounted DELL R730 system. The list below is not complete, as we only show the cost of the most important components. The idea is to focus on the total system price and show which components contribute the most to the total system cost.
| Xeon E7v3/POWER8 Price Comparison | ||||
| Feature | Dell R730 | IBM S822L | ||
| Type | Price | Type | Price | |
| Chassis | R730 | N/A | S822L | N/A |
| Processor | 2x E5-2697 | $5000 | 2x POWER8 3.42 | $3000 |
| RAM | 8x 16GB DDR4 DIMM |
$2150 | 8x 16 GB CDIMM (DDR3) | $8000 |
| PSU | 2x 1100W | $500 | 2x 1400W | $1000 |
| Disks | SATA or SSD | Starting at $200 |
SAS HD/SSD | +/- $450 |
| Total system price (approx.) | $10k | $15k | ||
With more or less comparable specs, the S822L was about 50% more expensive. However, it was almost impossible to make an apples-to-apples comparison. The biggest "price issue" are the CDIMMs, which are almost 4 times as expensive as "normal" RDIMMs. CDIMMs offer more as they include an L4-cache and some extra features (such as a redundant memory chip for each 9 chips). For most typical current Xeon E5 customers, the cost issue will be important. For a few, the extra redundancy and higher bandwidth will be interesting. Less important, but still significant is the fact that IBM uses SAS disks, which increase the cost of the storage system, especially if you want lots of them.
This cost issue will be much less important on most third party POWER8 systems. Tyan's "Habanero" system for example integrates the Centaur chips on the motherboard, making the motherboard more expensive but you can use standard registered DDR3L RDIMMs, which are much cheaper. Meanwhile the POWER8 processor tends to be very reasonably priced, at around $1500. That is what Dell would charge for an Intel Xeon E5-2670 (12 cores at 2.3-2.6 GHz, 120W). So while Intel's Xeon are much more power efficient than the POWER8 chips, the latter tends to be quite a bit cheaper.
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FunBunny2 - Friday, November 6, 2015 - link
"The z10 processor was co-developed with and shares many design traits with the POWER6 processor, such as fabrication technology, logic design, execution unit, floating-point units, bus technology (GX bus) and pipeline design style, i.e., a high frequency, low latency, deep (14 stages in the z10), in-order pipeline." from the Wiki.Yes, the z continues the CISC ISA from the 360 (well, sort of) rather than hardware RISC, but as Intel (amongst others) has demonstrated, CISC ISA doesn't have to be in hardware. In fact, the 360/30 (lowest tier) was wholly emulated, as was admitted then. Today, we'd say "micro-instructions". All those billions of transistors could have been used to implement X86 in hardware, but Intel went with emulation, sorry micro-ops.
What matters is the underlying fab tech. That's not going anywhere.
FunBunny2 - Friday, November 6, 2015 - link
^^ should have gone to KevinG!!Kevin G - Saturday, November 7, 2015 - link
The GX bus in the mainframes was indeed shared by POWER chips as that enabled system level component sharing (think chipsets).However, attributes like the execution unit and the pipeline depth are different between the POWER6 and z10. At a bird's eye view, they do look similar but the implementation is genuinely different.
Other features like SMT were introduced with the POWER5 but only the most recent z13 chip has 2 way SMT. Features like out-of-order execution, SMT, SIMD were once considered too exotic to validate in the mainframe market that needed absolute certainty in its hardware states. However, recent zArch chips have implemented these features, sometimes decades after being introduced in POWER.
The other thing is that IBM has been attempting to get get more and more of the zArch instruction set to be executed by hardware and no microcode. Roughly 75% to 80% of instructions are handled by microcode (there is a bit of a range here as some are conditional to use microcode).
JohanAnandtech - Saturday, November 7, 2015 - link
I believe that benchmark uses about 8 threads and not very well either? Secondly, it is probably very well optimized for SSE/AVX. So you can imagine that the POWER8 will not be very good at it, unless we manually optimize it for Altivec/VSX. And that is beyond my skills :-)UrQuan3 - Monday, December 21, 2015 - link
I'm sure no one is still reading this as I'm posting over a month later, but...I tested handbrake/x264 on a bunch of cross-platform builds including Raspberry Pi 2. I found it would take 24 RPi2s to match a single i5-4670K. That was a gcc compiled handbrake on Raspbian vs the heavily optimized DL copy for Windows. Not too bad really. Also, x264 seems to scale fairly well with the number of cores. Still, POWER8 unoptimized would be interesting, though not a fair test.
BTW, I'd encourage you to use a more standard Linux version than 6-month experimental little-endian version of Ubuntu. The slides you show advertise support for Ubuntu 14.04 LTS, not 15.04. For something this new, you may need the latest, but that is often not the case.
stun - Friday, November 6, 2015 - link
@Johan You might want to fix "the platform" hyperlink at the bottom of page 4. It is invalid.JohanAnandtech - Friday, November 6, 2015 - link
Thanks and fixed.Ahkorishaan - Friday, November 6, 2015 - link
Couldn't read past the graphic on page 1. It's 2015 IBM, time to use a font that doesn't look like a toddler's handwriting.xype - Sunday, November 8, 2015 - link
To be fair, it seems that the slide is meant for management types… :PJtaylor1986 - Friday, November 6, 2015 - link
Using decimals instead of commas to denote thousands is jarring to your North American readers.