问题
I'm compiling data to compare CPU and GPU GFLOP performance, and I'm looking currently at dual socket CPUs (E5-26xx family), however after Broadwell comes Skylake architecture which has Bronze and Silver dual processor families, but they have half the cores and performance than the Broadwell ones. Am I missing something?
回答1:
Interesting, it seems you're right that the only high-core-count Skylake-server chips are also capable of being used in 4-socket systems. (https://en.wikichip.org/wiki/intel/microarchitectures/skylake_(server)#Brands)
You can put Gold / Platinum CPUs in dual-socket systems. I assume most of what you're paying for in the high-core-count CPUs is the cores / cache themselves, so it's not a waste to use them in a 2-socket system.
SKX uses UPI instead of QPI as the interconnect between sockets. A CPU with 2 UPI links can be used in a 4P system, forming a ring instead of an all-to-all with 3 links in each CPU. Or a 2P system can use all 3 UPI links between the two sockets for more bandwidth. (Wikichip has diagrams)
Bronze / Silver, and Gold 5xxx CPUs have 2 UPI links, while Gold 6xxx and Platinum CPUs have 3 UPI links. (wikipedia)
Inside each Skylake-SP CPU (on a single die) the interconnect between cores is a mesh, vs. a ring bus in Broadwell and earlier.
4P/8P Broadwell (and earlier) Xeons have a small (14kiB? I can't find a more detailed description right now) snoop filter cache (see John McCalpin's post in this thread, but 2P chips don't, and just broadcast snoop requests to the other socket as they load from local DRAM, when a load misses in L3. This "uses a modest fraction of the QPI bandwidth". (The exact snoop behaviour is configurable with different modes to optimize for low-latency local memory vs. less-bad latency for remote memory, and so on).
Thus there is a hardware (not just artificial marketing / market-segmentation) difference between 2P and 4P/8P chips with the same core count for Broadwell and earlier.
Skylake-SP always has a snoop filter. See the Directory-Based Coherency section in Intel's paper on Skylake-Xeon internals.
(IDK the details. Maybe the Bronze/Silver chips are weaker, but their marketing department decided it wasn't worth doing finer-grained market segmentation within the Gold chips.)
回答2:
You do not miss anything in terms of Intel CPU generations code names, but your statement about "half the performance" is unclear. In particular, what exact SKUs do you compare? And, why did you choose to compare exactly that products of different generations? The official database is at http://ark.intel.com, there you can find models of the same market segments in different generations.
来源：https://stackoverflow.com/questions/48872306/what-comes-after-intel-xeon-broadwell-dual-processors