The Intel Xeon E7-8800 v3 Review: The POWER8 Killer?
by Johan De Gelas on May 8, 2015 8:00 AM EST- Posted in
- CPUs
- IT Computing
- Intel
- Xeon
- Haswell
- Enterprise
- server
- Enterprise CPUs
- POWER
- POWER8
The Competitor: IBM's POWER8
As we briefly mentioned in the introduction, among all of the potential competitors for the Xeon E7 line, IBM's OpenPower might be the most potent competitor at this time. So how do IBM's offerings compare to Intel's? IBM POWER 8 is a Brainiac (high IPC) design that also wants to be speed demon (high clock speeds).
The POWER8 core can decode, issue and execute and retire 8 instructions per cycle. That degree of of instruction level parallelism (ILP) can not be extracted out of (most) software. To battle the lack of ILP in software, no less than 8 threads (SMT) are active per core. According to IBM,
- 2-threads delivers about 45% performance more than one
- 4-threads deliver yet another 30% boost
- the last 4-threads deliver about 7%
So in total, the 8-way SMT doubles the performance of this massive core. Let us compare the two chips.
| Xeon E7v3/POWER8 Comparison | ||
| Feature | Intel Haswell-EX Xeon E7 |
IBM POWER8 |
| Process tech. | 22nm FinFET | 22nm SOI |
| Max clock | 2.5-3.6 GHz | 3.5-4.35 GHz |
| Max. core count Max. thread count |
18@2.5 GHz 36 SMT |
12@4.2 GHz 96 SMT |
| Max. sustained IPC | 6 (4) | 8 |
| L1-I / L1-D Cache | 32 KB/32 KB | 32 KB/64 KB |
| L2 Cache | 256 KB SRAM per core | 512 KB SRAM per core |
| L3 Cache | 2.5 MB SRAM per core | 8 MB eDRAM per core |
| L4 Cache | None | 16 MB eDRAM per MBC (64/128 MB total) |
| Memory | 1.5 TB per socket (64 GB per DIMM) |
1-2 TB per socket (64 GB per DIMM) |
| Theoretical Memory Bandwidth | 102 GB/s (independent mode) |
204 GB/s |
| PCIe 3.0 Lanes | 40 Lanes | 32 Lanes |
The POWER8 looks better than Haswell-EX in almost every spec, but the devil is of course in the details. First of all, Intel's L2-cache works at the same clock as the core, IBM's L2-cache runs at a lower clock (2.2 GHz or less, depending on the model). Secondly, the POWER8's L3 eDRAM cache might be much larger, but it is so also a bit slower.
But the main disadvantage of the POWER8 is that all this superscalar wideness and high clockspeed goodness comes with a power price. This slide from Tyan at the latest OpenPOWER conference tell us more.
A 12 core POWER8 is "limited" to 3.1 GHz if you want to stay below the 190W TDP mark. Clockspeeds higher than 4 GHz are only possible with 8-cores and a 250W TDP. This makes us really curious what kind of power dissipation we may expect from the 4.2 GHz 10-core POWER8 inside the expensive E870 Enterprise systems (300W?).
That is not all. Each "Jordan Creek2" memory buffer on the Intel system is limited to about 9W. IBM uses a similar but more complex "Centaur" memory buffer (including a 16 MB cache) which needs more than twice as much energy (16-20W). There are at least four of them per chip, and a high-end chip can have eight. So in total the Intel CPU plus memory buffers have a 201W TDP (165W CPU + 4x9W Jordan Creek 2), while the IBM platform has at best a 270W TDP (190W CPU+ 4x20W MBC).
Facebook
Twitter
RSS
146 Comments
View All Comments
DanNeely - Friday, May 8, 2015 - link
Intel's 94% market share is still only ~184k systems. That's tiny compared to the mainstream x86 market; and doesn't give a lot of (budgetary) room to make radical changes to CPU vs just scaling shared designs to a huger layout.theeldest - Friday, May 8, 2015 - link
184k for 4S systems. The number of 2S systems *greatly* outnumbers the 184k.Samus - Sunday, May 10, 2015 - link
by 100 orders of magnitude, easily.2S systems are everywhere these days, I picked up a Lenovo 2S Xeon system for $600 NEW (driveless, 4GB RAM) from CDW.
4S, on the other hand, is considerably more rare and starts at many thousands, even with 1 CPU included.
erple2 - Sunday, May 10, 2015 - link
Well, maybe 2 orders of magnitude. 100 orders of magnitude would imply, based on the 184k 4S systems, more 2S systems than atoms in the universe. Ok, I made that up, I don't know how many atoms are in the universe, but 10^100 is a really big number. Well, 10^105, if we assume 184k 4S systems.I think you meant 2 orders of magnitude.
mapesdhs - Sunday, May 10, 2015 - link
Yeah, that made me smile too, but we know what he meant. ;)evolucion8 - Monday, May 11, 2015 - link
That would be right if Intel cores are wide enough which aren't compared to IBM. For example, according to this review, enabling two way SMT boosted the performace to 45% and adding two more threads added 30% more performance. On the other hand, enabling two way SMT on the latest i7 architecture can only go up to 30% on the best case scenario.chris471 - Friday, May 8, 2015 - link
Great article, and I'm looking forward to see more Power systems.I would have loved to see additional benchmarks with gcc flags -march=native -Ofast. Should not change stream triad results, but I think 7zip might profit more on Power than on Xeon. Most software is not affected by the implied -ffast-math.
close - Friday, May 8, 2015 - link
It reminds me of the time when Apple gave up on PowerPC in mobiles because the new G5s were absolute power guzzlers and made space heaters jealous. And then gave up completely and switched to Intel because the 2 dual core PowerPC 970MP CPUs at 2.5GHz managed to pull 250W of power and needed liquid cooling to be manageable.IBM is learning nothing from past mistakes. They couldn't adapt to what the market wanted and the more nimble competition was delivering 25-30 years ago when fighting Microsoft, it already lost business to Intel (which is actually only nimble by comparison), and it's still doing business and building hardware like we're back in the '70s mainframe age.
name99 - Friday, May 8, 2015 - link
You are assuming that the markets IBM sells into care about the things you appear to care about (in particular CPU performance per watt). This is a VERY dubious assumption.The HPC users MAY care (but I'd need to see evidence of that). For the business users, the cost of the software running on these systems dwarfs the lifetime cost of their electricity.
SuperVeloce - Saturday, May 9, 2015 - link
They surely care. Why wouldn't they. A whole server rack or many of them in fact do use quite a bit of power. And cooling the server room is very expensive.