Sizing Up Servers: Intel's Skylake-SP Xeon versus AMD's EPYC 7000 - The Server CPU Battle of the Decade?
by Johan De Gelas & Ian Cutress on July 11, 2017 12:15 PM EST- Posted in
- CPUs
- AMD
- Intel
- Xeon
- Enterprise
- Skylake
- Zen
- Naples
- Skylake-SP
- EPYC
Introducing Skylake-SP: The Xeon Scalable Processor Family
The biggest news hitting the streets today comes from the Intel camp, where the company is launching their Skylake-SP based Xeon Scalable Processor family. As you have read in Ian's Skylake-X review, the new Skylake-SP core has been rather significantly altered and improved compared to it's little brother, the original Skylake-S. Three improvements are the most striking: Intel added 768 KB of per-core L2-cache, changed the way the L3-cache works while significantly shrinking its size, and added a second full-blown 512 bit AVX-512 unit.
On the defensive and not afraid to speak their mind about the competition, Intel likes to emphasize that AMD's Zen core has only two 128-bit FMACs, while Intel's Skylake-SP has two 256-bit FMACs and one 512-bit FMAC. The latter is only useable with AVX-512. On paper at least, it would look like AMD is at a massive disadvantage, as each 256-bit AVX 2.0 instruction can process twice as much data compared to AMD's 128-bit units. Once you use AVX-512 bit, Intel can potentially offer 32 Double Precision floating operations, or 4 times AMD's peak.
The reality, on the other hand, is that the complexity and novelty of the new AVX-512 ISA means that it will take a long time before most software will adopt it. The best results will be achieved on expensive HPC software. In that case, the vendor (like Ansys) will ask Intel engineers to do the heavy lifting: the software will get good AVX-512 support by the expensive process of manual optimization. Meanwhile, any software that heavily relies on Intel's well-optimized math kernel libraries should also see significant gains, as can be seen in the Linpack benchmark.
In this case, Intel is reporting 60% better performance with AVX-512 versus 256-bit AVX2.
For the rest of us mere mortals, it will take a while before compilers will be capable of producing AVX-512 code that is actually faster than the current AVX binaries. And when they do, the result will be probably be limited, as compilers still have trouble vectorizing code from scratch. Meanwhile it is important to note that even in the best-case scenario, some of the performance advantage will be negated by the significantly lower clock speeds (base and turbo) that Intel's AVX-512 units run at due to the sheer power demands of pushing so many FLOPS.
For example, the Xeon 8176 in this test can boost to 2.8 GHz when all cores are active. With AVX 2.0 this is reduced to 2.4 GHz (-14%), with AVX-512, the clock tumbles down to 1.9 GHz (another 20% lower). Assuming you can fill the full width of the AVX unit, each step still sees a significant performance improvement, but AVX2 to AVX-512 won't offer a full 2x performance improvement even with ideal code.
Lastly, about half of the major floating point intensive applications can be accelerated by GPUs. And many FP applications are (somewhat) limited by memory bandwidth. While those will still benefit from better AVX code, they will show diminishing returns as you move from 256-bit AVX to 512-bit AVX. So most FP applications will not achieve the kinds of gains we saw in the well-optimized Linpack binaries.
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ddriver - Tuesday, July 11, 2017 - link
Gotta love the "you don't care about the xeon prices" part thou. Now that intel don't have a performance advantage, and their product value at the high end is half that of amd, AT plays the "intel is the better brand" card. So expected...OZRN - Wednesday, July 12, 2017 - link
You need some perspective. Database licensing for Oracle happens per core, where Intel's performance is frequently better in a straight line and since they achieve it on lower core count it's actually better value for the use case. Higher per-CPU cost is not so much of a concern when you pay twice as much for a processor license to cover those cores.I'm an AMD fan and I made this account just for you, sweetheart, but don't blind yourself to the truth just because Intel has a history of shady business. In most regards this is a balanced review, and where it isn't, they tell you why it might not be. Chill out.
ddriver - Thursday, July 13, 2017 - link
You are such a clown. Nobody, I repeat, NOBODY on this planet uses 64 core 128 thread 512 gigabytes of ram servers to run a few MB worth of database. You telling me to get pespective thus can mean only two things, that you are a buthurt intel fanboy troll or that you are in serious need of head examination. Or maybe even both. At any rate, that perfectly explains your ridiculously low standards for "balanced review".Notmyusualid - Friday, July 14, 2017 - link
It seems no matter what opinion someone presents that might exhibit Intel in a better light - you are going to hate it anyway.What a life you must lead.
OZRN - Friday, July 14, 2017 - link
No, they don't. They use them to host gigabytes to terabytes worth of mission critical databases, with specified amounts of cores dedicated to seperate environments of hard partitioned data manipulation. I've done some quick math for you and in an average setup of Enterprise Edition of Oracle DB, with only the usually reported options and extras, this type of database would cost over $3.7m to run on *64 cores alone*. At this point, where is your hardware sunk costs argument?Also, I don't think anyone here is impressed by your ability to immediately personally insult people making valid points. Good luck finding your head that deep in your colon.
CajunArson - Tuesday, July 11, 2017 - link
"All of our testing was conducted on Ubuntu Server "Xenial" 16.04.2 LTS (Linux kernel 4.4.0 64 bit). The compiler that ships with this distribution is GCC 5.4.0."I'd recommend using a more updated distro and especially a more up to date compiler (GCC 5.4 is only a bug-fix release of a compiler from *2015*) if you want to see what these parts are truly capable of.
Phoronix does heavy-duty Linux reviews and got some major performance boosts on the i9 7900X simply by using up to date distros: http://www.phoronix.com/scan.php?page=article&...
Considering that Purley is just an upscaled version of the i9 7900X, I wouldn't be surprised to see different results.
CajunArson - Tuesday, July 11, 2017 - link
As a followup to my earlier comment, that Phoronix story, for example, shows a speedup factor of almost 5X on the C-ray benchmark simply by using a modern distro with some tuning for the more modern Skylake architecture.I'm not saying Purley would have a 5X speedup on C-ray per-say, but I'd be shocked if it didn't get a good boost using modern software that's actually designed for the Skylake architecture.
CoachAub - Wednesday, July 12, 2017 - link
Keywords: "actually designed for the Skylake architecture". Will there be optimizations for AMD Epyc chips?mkozakewich - Friday, July 14, 2017 - link
If it's a reasonable optimization, it makes sense to include it in the benchmark. If I were building these systems, I'd want to see benchmarks that resembled as closely as possible my company's workflow. (Which may be for older software or newer software; neither are inherently more relevant, though benchmarks on newer software will usually be relevant further into the future.)CajunArson - Tuesday, July 11, 2017 - link
And another followup: The time kernel compilation on the i9 7900X got almost a factor of 2 speedup over the Ubuntu 16.04 using more modern distros.