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Comment by tmd83 | Hacker News Reader

This is quite surprising. I assumed they would get an EPYC server with higher core at similar price (due to the cost of the CPU) and get advantage in performance/dollar. I didn't expect EPYC to beat a similar physical core count intel server running at similar core count let alone by this much margin. Am I missing something here?

I'm saying this as someone who really wants AMD to succeed and push the ecosystem forward. I just want to make sure that I'm reading the results correctly here.

They are effectively getting 35% extra performance 60% of the price that's just beyond impressive.

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EPYC is compared to a previous generation Xeon with lower TDP (105w vs 155/170w) and slower RAM (2400 vs 2666). The Xeon server is more expensive probably because it has 4x the amount of RAM.

Edit: actually, this is a dual Xeon machine so its TDP is slightly higher than EPYC's.

Doesn't that make it more impressive? The AMD build has a quarter of the RAM and still came out ahead!?

Unsurprisingly, the amount of RAM has little effect on a CPU-heavy workload.

For this workload, they could have had 16 GiB of RAM and get pretty much identical results.

> EPYC is compared to a previous generation Xeon with lower TDP ... Edit: actually, this is a dual Xeon machine so its TDP is slightly higher than EPYC's.

Comparing TDPs between manufacturers is invalid.

> Comparing TDPs between manufacturers is invalid.

Why? It's all Watts

"TDP" is not a figure resulting from a standardized process. Each manufacturer has a different (and sometimes changing) definition of it. E.g. for Intel it is a supposed power consumption given a certain load at base clock. Meanwhile with AMD it basically encodes the standard thermal parameters (Tamb, Tj(max), Rthjc).

«EPYC is compared to a previous generation Xeon»

That's not enough to explain. I highly doubt replacing the 12-core Broadwell Xeon CPUs with a current-generation 12-core Xeon (which would be Skylake) would catch up with the 30-40% performance lead that EPYC displays in their workload.

The Zen microarchitecture of the EPYC is quite impressive and it could just very well be a workload that Zen is particularly good at.

For example the fact EPYC can pack so many cores on a single socket means all the RAM and all its 64MB of last-level cache are "local" to every core (at worst accesses go through the Infinity Fabric.) By comparison, in Intel's case when one of the Xeon cores need to access RAM or cache on the other socket, accesses have to go through the QPI link between the 2 sockets, and it has higher latencies and worse throughput than AMD EPYC's Infinity Fabric.

>They are effectively getting 35% extra performance 60% of the price that's just beyond impressive.

Lets just ignore the price point for now because the memory capacity are different.

But the performance, 24 Core AMD EPYC Zen is ~35% faster than 24 Core Intel Broadwell Xeon under the same frequency? Broadwell isn't even that old because Intel has only launched Skylake Xeon E5 not long ago. And the different between Skylake and Broadwell IPC aren't that much either. the max turbo speed are similar, and the Intel platform had the advantage of two CPU using two heatsink, higher TDP, higher heat dissipation more time for turbo.

And most testing has shown Zen to be about Sandybridge IPC performance. Something seems wrong here ( Or may be too good to be true )

I suspect that the Xeon processors are running at a lower frequency under load compared to the EPYC ones.

That's just a hunch though.

It isn't, because according to the spec sheet its all Core frequency are about the same as AMD.

Maybe their workloads were I/O bound and the EPYC server has faster SSDs?

The EPYC has twice as many memory busses.

False. The E5-2650 v4 has four memory channels, and with two sockets populated, you get eight memory channels, same as EPYC.

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