Home / server / Questions / 787313
Accepted
bwDraco
Asked: 2016-07-01 22:25:37 +0800 CST

Intel Xeon processors: Difference between 2S/4S and S2S/S4S scalability

  • 772

While comparing Intel Xeon E5 and E7 processors, I've noticed that E5 processors are specified for 2S or 4S scalability, while E7 processors are specified for S2S, S4S, or S8S scalability.

I understand that the processors are specified for use in up to the given number of sockets on the same motherboard, but what does the extra S actually mean? What's the difference between 2S and S2S, and between 4S and S4S?

central-processing-unit hardware scalability xeon

2 Answers

  1. Based on "6.5.8.4 MPSUP: Multiprocessor Support" in Intel® Xeon® Processor E7-4800/8800 v3 Product Families; Datasheet - Volume 1: Electrical, Mechanical and Thermal (pdf, page 139):

    This location contains 2 bits for representing the supported number of physical processors on the bus. These two bits are LSB aligned where 00b equates to nonscalable 2 socket (2S) operation, 01b to scalable 2 socket (S2S), 10 to scalable 4 socket (S4S), and scalable 8 socket (S8S). The Intel® Xeon® E7 v3 processor is a S2S, S4S, or S8S processor. The first six bits in this field are reserved for future use. Writes to this register have no effect.

    • S prefix:
      • Exists: Scalable (based on the language, I believe this means you can use fewer processors)
      • Missing: Nonscalable (you must have the specified number of processors)
    • Number:
      • Number of processors (if scalable, this is maximum number of processors; if nonscalable, this is the required number of processors)
    • S postfix:
      • Stands for "socket"

    So, for example, S4S is "scalable four socket" and 2S is "nonscalable two socket".

    • 10
  2. Best Answer

    The difference between S4S and 4S is the number of QPI-Links. 4S has 2 links per CPU, S4S and S8S have 3.

    On a 4S system CPUs form a ring, which means for every CPU there is another CPU with which it can only communicate indirectly, because it is only connected to 2 CPUs via QPI.

    On S4S every CPU is directly connected to every other CPU.

    For S8S there are also 3 QPI links.

    Question is a little older, but maybe my answer is still relevant.

    • 10