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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 becau

by boris 8y ago

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.

yjftsjthsd-h 8y ago
Doesn't that make it more impressive? The AMD build has a quarter of the RAM and still came out ahead!?
- wereHamster 8y ago
  Unsurprisingly, the amount of RAM has little effect on a CPU-heavy workload.
- stefan_ 8y ago
  For this workload, they could have had 16 GiB of RAM and get pretty much identical results.
blattimwind 8y ago
> 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.
- kingbirdy 8y ago
  > Comparing TDPs between manufacturers is invalid. Why? It's all Watts
  - blattimwind 8y ago
    "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).
mrb 8y ago
«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.

by boris 8y ago

yjftsjthsd-h 8y ago

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

wereHamster 8y ago
Unsurprisingly, the amount of RAM has little effect on a CPU-heavy workload.
stefan_ 8y ago
For this workload, they could have had 16 GiB of RAM and get pretty much identical results.

blattimwind 8y ago

> 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.

kingbirdy 8y ago
> Comparing TDPs between manufacturers is invalid. Why? It's all Watts
- blattimwind 8y ago
  "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).

mrb 8y ago

«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.