Assessing IBM's POWER8, Part 1: A Low Level Look at Little Endian
by Johan De Gelas on July 21, 2016 8:45 AM ESTBenchmark Selection
Our testing was conducted on Ubuntu Server 15.10 (kernel 4.2.0) with gcc compiler version 5.2.1.
The choice of comparing the IBM POWER8 2.92 10-core with the Xeon E5-2699 v4 22-core might seem weird, as the latter is three-times as expensive as the former. However, for this review, where we evaluate single thread/core performance, pricing does not matter. As this is one of the lowest clocked POWER8 CPUs, an Intel Xeon with a high base clock - something that's common for Intel's chips with fewer cores - would make it harder to compare the two microarchitectures. We also wanted an Intel chip that could reach high turbo clockspeeds thanks to a high TDP.
And last but not least we did not have very many Xeon E5 v4 SKUs in the lab...
Configuration
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.
| CPU | One IBM POWER8 2.92 GHz (up to 3.5 GHz Turbo) |
| RAM | 256 GB (16x16GB) DDR3-1333 |
| Internal Disks | 2x Samsung 850Pro 960 GB |
| Motherboard | Tyan SP012 |
| PSU | Delta Electronics DSP-1200AB 1200W |
Intel's Xeon E5 Server – S2600WT (2U Chassis)
This is the same server that we used in our latest Xeon v4 review.
| CPU |
Xeon E5-2699 v4 |
| RAM | 256 GB (8x32GB) Samsung DDR4-2400 |
| Internal Disks | 2x Samsung 850Pro 960 GB |
| Motherboard | Intel Server Board Wildcat Pass |
| PSU | Delta Electronics 750W DPS-750XB A (80+ Platinum) |
Hyperthreading, Turbo, C1 and C6 were enabled in the BIOS.
Other Notes
All 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 in our Sizing Servers Lab.
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HellStew - Wednesday, July 27, 2016 - link
It depends what kind of software you are running. If you are running giant backend workloads on x86, you can seamlessly migrate that data to PPC while keeping custom front ends running on x86.aryonoco - Saturday, July 23, 2016 - link
Johan, maybe the little endian-ness makes a difference in porting proprietary software, but pretty much all open source software on Linux has supported BE POWER for a long time.If you get the time and the inclination Johan, it would be great if you could say do some benchmarks on BE RHEL 7 vs LE RHEL 7 on the same POWER 8 system. I think it would make for fascinating reading in itself, and would show if there are any differences when POWER operates in BE mode vs LE mode.
aryonoco - Saturday, July 23, 2016 - link
Actually scrap that, seems like IBM is fully focusing on LE for Linux on POWER in future. I'm not sure there will be many BE Linux distributions officially supporting POWER9 anyway. So your choice of focusing on LE Linux on POWER is fully justified.HellStew - Wednesday, July 27, 2016 - link
Side note: Once you are running KVM, you can run any mix of BE and LE linux varieties side by side. I'm running FedoraBE, SuSE BE, Ubuntu LE, CentOS LE, and (yes a very slow copy of windows) on one of these chipsrootbeerrail - Saturday, July 23, 2016 - link
If a machine is completely isolated, it doesn't matter much to the machine. I personally find BE easier to read in hex dumps because it follows the left-to-right nature of English numbers, but there are reasons to use LE for human understanding as well.The problem shows up the instance one tries to interchange binary data. If the endian order does not match, the data is going to get scrambled. Careful programming can work around this issue, but not everyone is a careful programmer - there's a lot of 'get something out the door' from inexperienced or lazy people. If everything is using the same conventions (not only endian, but size of the binary data types (less of a problem now that most everything has converged to 64-bit)), it's not an issue. Thus having LE on Power makes the interchange of binary data easier with the X86 world.
errorr - Friday, July 22, 2016 - link
Great Article! Just an FYI, the term "just" as in "just out" on the first page has different meanings on opposite sides of the Atlantic and is usually avoided in writing for international audiences. I'm not quite sure which one is used her. The NaE would mean 'just out' in that it had come out right before while the BrE would mean it came out right after the time period referenced in the sentence.xCalvinx - Friday, July 22, 2016 - link
awesome!!..keepup the good work..looking forward to Part2!! ... actualy cant wait.. hurryup lol.. :)double thumbsup
Mpat - Friday, July 22, 2016 - link
Skylake does not have 5 decoders, it is still 4. I know that that segment of the optimization manual is written in a cryptic way, but this's what actually happened: up until Broadwell there are 4 decoders and a max bandwidth from the decoder segment of 4 uops. If the first decoder (the complex one) produces 4 uops from one x86 op, the other decoders can't work. If the first produces 3, then the second can produce 1, etc. this means that the decoders can produce one of these combinations of uops from an x86 op, depending on how complex a task the first decoder has: 1/1/1/1, 2/1/1, 3/1, or 4. Skylake changes this so the max bandwidth from that segment is now 5, and the legal combinations become 1/1/1/1, 2/1/1/1, 3/1/1, and 4/1. You still can't do 1/1/1/1/1, so there is still only 4 decoders. Make sense?ReaperUnreal - Friday, July 22, 2016 - link
Why do the tests with GCC? Why not give each platform their full advantage and go with ICC on Intel and xLC on Power? The compiler can make a HUGE difference with benchmarks.Michael Bay - Saturday, July 23, 2016 - link
It`s right in the text why.