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
Intel’s Turbo Modes
A last minute detail from Intel yesterday was information on the Turbo modes. As expected, not all of the processors actually run at their rated/base frequency: most will apply a series of turbo modes depending on how many cores are registered as ‘active’. Each core can have its frequency adjusted independently, allowing VMs to take advantage of different workload types and not be hamstrung by occupants on other VMs in the same socket. This becomes important when AVX, AVX2 and AVX-512 are being used at the same time.
Most of the turbo modes are a sliding scale, with the peak turbo used when only one or two cores are active, sliding down to a minimum frequency that may be the ‘base’ frequency or just above it. There’s a lot of information for the parts here, so we’ll break it down into stages.
First up, a look at the Platinum 8180 in the different modes:
It should be worth noting what the base frequency actually is, and some of the nuance in Intel’s wording here. The base frequency is the guaranteed frequency of the chip – Intel sells the chip with the base frequencies as the guarantee, such that when the chip is not idle and not in normal conditions (i.e. when not in thermal power states to reduce temperature) should operate at this frequency or above it. Intel also lists the per-core turbo frequencies as ‘Maximum Core Frequencies’ indicating that the processors could be running lower than listed, depending on power distribution and requirements in other areas of the chip (such as the uncore, or memory controller). It’s a vague set of terms but ultimately the frequency is determined on the fly and can be affected by many factors, but Intel guarantees a certain amount and provides guides as to what it expects the turbo frequencies to be.
As for the Platinum 8180, it keeps its top turbo modes while up to two cores are active, and then drops down. It does this again for another two cores, and a further two cores. From this point, under non-AVX load the CPU is pretty much the same frequency until >20 cores are loaded, but does not decrease that much in all. For AVX 2.0 and AVX-512, the downward slope of more cores means less frequency continues, with AVX-512 taking a bigger jump down at 13 cores loaded. The final turbo frequency for AVX-512 running on all cores is 2.3 GHz.
Comparing the two 28-core CPUs for which we have turbo information gives this graph. The numbers relate to the number of cores need to be loaded for that frequency.
Both processors are equal to each other for dual core loading, but the separation occurs when more cores are loaded. As we move through to AVX 2.0 and AVX-512, it is clear where the separations are in performance – to get the best for variable core loading, the more expensive processors are required.
Here’s the big table for all the processors on Non-AVX loading:
Despite the 2.0/2.1 GHz base on most of the Platinum series, all the CPUs will turbo up to 3.7-3.8 GHz on low core loading except for the lower power Platinum 8153. For users wanting to strike a good balance between the core count and frequency, the Gold 6154 is probably the place to be: 18 cores that will only ever run at 3.7 GHz with non-AVX loading (3.5-2.7 GHz on AVX-512 depending on core count), and will be $3543 as a list price at 205W. It is perhaps worth noting that this will likely top any of the Core i9 processors planned: at 18-cores and 205W for 3.7 GHz, the Core i9-7980XE which will have 18 cores but run 165W will likely be clocked lower (but also only ~$2000).
Moving onto AVX2.0 and AVX-512:
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PixyMisa - Tuesday, July 11, 2017 - link
No, the pricing is correct. The 1P CPUs really are half the price of a single 2P CPU.msroadkill612 - Wednesday, July 12, 2017 - link
Seems to me, the simplest explanation of something complex, is to list what it will not do, which they will not do :(.Can i run a 1p Epyc in a 2p mobo e.g., please?
PixyMisa - Thursday, July 13, 2017 - link
Short answer is no. It might boot, but only half the slots, memory, SATA and so on will be available. Two 1P CPUs won't talk to each other.A 2P Epyc will work in a 1P board though.
cekim - Tuesday, July 11, 2017 - link
One glaring bug/feature of AMD's segmentation relative to Intel's is the utter and obvious crippling of clock speeds for all but the absolute top SKUs. Fewer cores should be able to make use of higher clocks within the same TDP envelope. As a result Intel is objectively offering more and better fits up and down the sweep of cores vs clocks vs price spectrum.So, the bottom line is AMD is saying that you will have to buy the top-end, 4S SKU to get the top GHz for those applications in your mix that won't benefit from 16,18,32,128 cores.
I say all of this as someone who desperately wants EPYC to shake things up and force Intel to remove the sand-bags. I know I'm in a small, but non-zero market of users who can make use of dozens of cores, but still need 8 or fewer cores to perform on par with desktop parts for that purpose.
KAlmquist - Wednesday, July 12, 2017 - link
One possibility is that they have only a small percentage of the chips currently being produced bin well enough to be used in the highest clocking SKU's, so they are saving those chips for the most expensive offerings. Admittedly, that depends on what they are seeing coming off the production line. If they have a fair number of chips where with two very good cores, and two not so good, then it would make sense to offer a high clocking 16 core EPYC using chips with two cores disabled. But if clock speed on most chips is limited due to minor registration errors (which would affect the entire chip), then a chip with only two really good cores would require two localized defects in two separate cores, in addition to very good registration to get the two good cores. The combination might be too rare to justify a separate SKU.I would expect Global Foundries to continue to tweak its process to get better yields. In that case, more processors would end up in the highest bin, and AMD might decide to launch a higher clock speed 16 and 8 core EPYC processors, mostly using chips which bin well enough that they could have been used for the 32 core EPYC 7601.
alpha754293 - Tuesday, July 11, 2017 - link
Why does the Intel Xeon 6142 cost LESS than the 6142M? (e.g. per the table above, 6142 is shown with a price of $5946 while the 6142M costs $2949)ca197 - Tuesday, July 11, 2017 - link
I assume that is the wrong way round on the list. I have seen it reported the other way round on other sites.Ian Cutress - Tuesday, July 11, 2017 - link
You're correct. I've updated the piece, was a misread error from Intel's tables.coder543 - Tuesday, July 11, 2017 - link
On page 6, it says that Epyc only has 64 PCIe lanes (available), but that's not correct. There are 128 PCIe lanes per chip. In a 1P configuration, that's 128 PCIe lanes available. On a 2P configuration, 64 PCIe lanes from each chip are used to connect to the other chip, leaving 64 + 64 = 128 PCIe lanes still available.This is a significant advantage.
Ian Cutress - Tuesday, July 11, 2017 - link
You misread that table. It's quoting per-CPU when in a 2P configuration.