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
Memory Subsystem: Bandwidth
Measuring the full bandwidth potential with John McCalpin's Stream bandwidth benchmark is getting increasingly difficult on the latest CPUs, as core and memory channel counts have continued to grow. We compiled the stream 5.10 source code with the Intel compiler (icc) for linux version 17, or GCC 5.4, both 64-bit. The following compiler switches were used on icc:
icc -fast -qopenmp -parallel (-AVX) -DSTREAM_ARRAY_SIZE=800000000
Notice that we had to increase the array significantly, to a data size of around 6 GB. We compiled one version with AVX and one without.
The results are expressed in gigabytes per second.
Meanwhile the following compiler switches were used on gcc:
-Ofast -fopenmp -static -DSTREAM_ARRAY_SIZE=800000000
Notice that the DDR4 DRAM in the EPYC system ran at 2400 GT/s (8 channels), while the Intel system ran its DRAM at 2666 GT/s (6 channels). So the dual socket AMD system should theoretically get 307 GB per second (2.4 GT/s* 8 bytes per channel x 8 channels x 2 sockets). The Intel system has access to 256 GB per second (2.66 GT/s* 8 bytes per channel x 6 channels x 2 sockets).
AMD told me they do not fully trust the results from the binaries compiled with ICC (and who can blame them?). Their own fully customized stream binary achieved 250 GB/s. Intel claims 199 GB/s for an AVX-512 optimized binary (Xeon E5-2699 v4: 128 GB/s with DDR-2400). Those kind of bandwidth numbers are only available to specially tuned AVX HPC binaries.
Our numbers are much more realistic, and show that given enough threads, the 8 channels of DDR4 give the AMD EPYC server a 25% to 45% bandwidth advantage. This is less relevant in most server applications, but a nice bonus in many sparse matrix HPC applications.
Maximum bandwidth is one thing, but that bandwidth must be available as soon as possible. To better understand the memory subsystem, we pinned the stream threads to different cores with numactl.
| Pinned Memory Bandwidth (in MB/sec) | |||
| Mem Hierarchy |
AMD "Naples" EPYC 7601 DDR4-2400 |
Intel "Skylake-SP" Xeon 8176 DDR4-2666 |
Intel "Broadwell-EP" Xeon E5-2699v4 DDR4-2400 |
| 1 Thread | 27490 | 12224 | 18555 |
| 2 Threads, same core same socket |
27663 | 14313 | 19043 |
| 2 Threads, different cores same socket |
29836 | 24462 | 37279 |
| 2 Threads, different socket | 54997 | 24387 | 37333 |
| 4 threads on the first 4 cores same socket |
29201 | 47986 | 53983 |
| 8 threads on the first 8 cores same socket |
32703 | 77884 | 61450 |
| 8 threads on different dies (core 0,4,8,12...) same socket |
98747 | 77880 | 61504 |
The new Skylake-SP offers mediocre bandwidth to a single thread: only 12 GB/s is available despite the use of fast DDR-4 2666. The Broadwell-EP delivers 50% more bandwidth with slower DDR4-2400. It is clear that Skylake-SP needs more threads to get the most of its available memory bandwidth.
Meanwhile a single thread on a Naples core can get 27,5 GB/s if necessary. This is very promissing, as this means that a single-threaded phase in an HPC application will get abundant bandwidth and run as fast as possible. But the total bandwidth that one whole quad core CCX can command is only 30 GB/s.
Overall, memory bandwidth on Intel's Skylake-SP Xeon behaves more linearly than on AMD's EPYC. All off the Xeon's cores have access to all the memory channels, so bandwidth more directly increases with the number of threads.
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deltaFx2 - Thursday, July 13, 2017 - link
"Can you mention one innovation from AMD that changed the world?" : None. But the same applies to Intel too, save, I suppose, the founders (Moore and Noyce) contributions to IC design back when they were at Fairchild/Shockley. That's not Intel's contribution. Computer Architecture/HPC? That's IBM. They invented the field along with others like CDC. Intel is an innovator in process technology, specifically manufacturing. Or used to be... others are catching up. That 3-yr lead that INtel loves to talk about is all but gone. So with that out of the way...AMD's contributions to x86 technology: x86-64, hypertransport, integrated memory controller, multicore, just to name a few. Intel copied all of them after being absolutely hammered by Opteron. Nehalem system architecture was a copy-paste of Opteron. It is to AMD's discredit that they ceded so much ground on the CPU microarchitecture since then with badly executed Bulldozer, but it was AMD that brought high-performance features to x86 server. Intel would've just loved to keep x86 on client and Itanium on server (remember that innovative atrocity?). Then there's a bunch on the GPU side (which INtel can't get right for love or money), but that came from an acquisition, so I won't count those.
"AMD exists because they are always inferior". Remember K8? It absolutely hammered intel until 2007. Remember Intel's shenanigans bribing the likes of Dell to not carry K8? Getting fined in the EU for antitrust behaviors and settling with AMD in 2010? Not much of a memory card on you, is there?
AMD gaining even 5-10% means two things for intel: Lower margins on all but the top end (Platinum) and a loss in market share. That's plain bad for the stock.
"Intel is a data center giant have head start have the resources...". Yes, they are giants in datacenter compute. 99% market share. Only way to go from there is down. Also, those acquisitions you're talking about? Only altera applies to the datacenter. Also, remember McAfee for an eye-watering $7.8 bn? How's that working out for them?
Shankar1962 - Wednesday, July 12, 2017 - link
Nvidia who have been ahead than Intel in AI should be the more competent threatHow much market share Intel loses depends on how they compete against Nvidia
Amd will probably gain 5% by selling products for cheap prices
Intel controls 98/99% share so it's inevitable to lose a few % as more players see the money potential but unless Intel loses to Nvidia there is annuphill battle for Qualcomm ARM.
HanSolo71 - Wednesday, July 12, 2017 - link
Could you guys create a Benchmark for Virtual Desktop Solutions? These AMD chips sound awesome for something like my Horizon View environment where I have hundreds of 2 core 4GB machines.Threska - Saturday, July 22, 2017 - link
For VDI wouldn't either an APU setup, or CPU+GPU be better?msroadkill612 - Wednesday, July 12, 2017 - link
Kudos to the authors. I imagine its gratifying to have stirred such healthy & voluminous debate :)milkod2001 - Thursday, July 13, 2017 - link
Are you guys still updating BENCH results? I cannot find there benchmark results for RYZEN CPUs when i want to compare them to others.Ian Cutress - Friday, July 14, 2017 - link
They've been there since the launchAMD (Zen) Ryzen 7 1800X:
http://www.anandtech.com/bench/product/1853
KKolev - Thursday, July 13, 2017 - link
I wonder if AMD'd EPYC CPU's can be overclocked. If so, the AMD EPYC 7351P would be very interesting indeed.uklio - Thursday, July 13, 2017 - link
How could you not do Cinebench results?! we need an answer!JohanAnandtech - Thursday, July 13, 2017 - link
I only do server benchmarks, Ian does workstation. Ian helped with the introduction, he will later conduct the workstation benchmarks.