Assessing IBM's POWER8, Part 1: A Low Level Look at Little Endian
by Johan De Gelas on July 21, 2016 8:45 AM ESTSystem Specs
Lastly, let's take a look at some high level specs. It is interesting to note that the IBM POWER8 inside our S812LC server is a 10-core Single Chip Module. In other words it is a single 10-core die, unlike the 10-core chip in our S822L server which was made of two 5-core dies. That should improve performance for applications that use many cores and need to synchronize, as the latency of hopping from one chip to another is tangible.
The SKU inside the S812LC is available to third parties such Supermicro and Tyan. This cheaper SKU runs at "only" 2.92 GHz, but will easily turbo to 3.5 GHz.
| Feature | IBM POWER8 (Available in LC servers) |
Intel Broadwell (Xeon E5 v4) |
| Process tech. | 22nm SOI | 14nm FinFET |
| Max clock | 2.92-3.5 GHz | 2.2-3.6 GHz |
| Max. core count Max. thread count |
10@2.92 GHz (3.5 GHz Turbo) 80 SMT |
22@2.2 GHz (2.8 GHz turbo) 44 SMT |
| TDP | 190W | 145W |
| L1-I / L1-D Cache | 32 KB/64 KB | 32 KB/32 KB |
| L2 Cache | 512 KB SRAM per core | 256 KB SRAM per core |
| L3 Cache | 8 MB eDRAM per core | 2.5 MB SRAM per core |
| L4 Cache | 16 MB eDRAM per MBC (64 MB total) |
None |
| Memory | 1 TB per socket - 32 slots (32 GB per DIMM) |
0.768 TB per socket - 12 slots (64 GB per DIMM) |
| Theoretical Memory Bandwidth | 76.8 GB/s Read 38.4 GB/s Write |
76.8 GB/s Read or Write |
| PCIe 3.0 Lanes | 32 Lanes | 40 Lanes |
The Xeon and IBM POWER8 have totally different memory subsystems. The IBM POWER8 connects to 4 "Centaur" buffer cache chips, which have each a 19.2 GB/s read and 9.6 GB/s write link to the processor, or 28.8 GB/s in total. This is a more efficient connection than the Xeon which has a simpler half-duplex connection to the RAM: it can either write with 76.8 GB/s to the 4 channels or read from the 4 channels. Considering that reads happen twice as much as writes, the IBM architecture is - in theory - better balanced and has more aggregated bandwidth.
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DomOfSF - Thursday, July 21, 2016 - link
Johan de Gelas: blowing minds and educating "the rest of us" since...I dunno, a really long time ago (especially in internet years). Great job on the data, but the real good stuff is in your thoughts and analysis. Thank you!close - Saturday, July 23, 2016 - link
Over a decade...JohanAnandtech - Thursday, July 28, 2016 - link
13 years in the server business, 18 years now of reviewing hardware :-). Thx !!jamyryals - Thursday, July 21, 2016 - link
It seems to me, Intel's focus on bringing their CPU architecture design all the way down to 5W is the reason IBM is able to stand out against them. Intel is focused on creating a scalable architecture while IBM can throw the whole kitchen sink at the server market.Fascinating article, I really enjoyed it.
smilingcrow - Thursday, July 21, 2016 - link
Intel has plenty of unique features in their server platforms which aren't in the consumer platforms so I don't think that is the issue.jospoortvliet - Tuesday, July 26, 2016 - link
The basic design of the core still is the same so there is probably at least some truth in the statement of Jamy.Kevin G - Wednesday, July 27, 2016 - link
Up until this point. Consumer SkyLake and server SkyLake are going to be two different designs. They're certainly related but server SkyLake will have 512 KB of L2 cache per core and support AVX-512 instructions.Server SkyLake is also going to support 3D Xpoint DIMMs, though that difference is more with the platform/chipset than the actual CPU core.
floobit - Thursday, July 21, 2016 - link
Very interesting. It seems odd to me that they chose to configure it in a 2U - except for big data clusters, most of the market space I see this playing is dominated by FC to a SAN. Is this a play in the big data cluster space, or the more traditional AIX/DB2/big iron that IBM has owned for so long?Some questions I'd have:
what virtualization is possible with this architecture? presumably just the standard PowerVM? How well does that work?
What is the impact of IO latency? Could you throw a P3700 or two in here?
JohanAnandtech - Thursday, July 21, 2016 - link
2U: Besides big data storage needs, I suspect 2U is necessary for adequate cooling for the POWER8 chip.Virtualization: Linux KVM works well as far as I know.
We actually tried out a P3700 in there (see: http://www.anandtech.com/show/9567/the-power-8-rev... ) and it worked very well. I asked IBM what a customer should expect when using third party storage (probably no support, but how about waranty?) but no answer yet.
mystic-pokemon - Friday, July 22, 2016 - link
Hi Johan2U is not necessary for cooling a POWER 8 Chip. We do that better with our Barreleye (1.25 OU design). Even storage wise Barreleye has 15 Disk storage bay that can be seen in below links.
http://www.v3.co.uk/v3-uk/news/2453992/google-and-...
Let me know if you wanna ever benchmark a Barreleye. What specific POWER8 proc are you benchmarking with ? (Turismo?). I believe it does slightly better than S812LC on many benchmarks based on the variant of power8 proc S812LC runs.