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My system has an Intel Xeon Processor E5-2630 v3 (8 cores, 2 threads/core). According to the Intel web page, there are 2 QPI links.

Nevertheless, when running the pcm-pcie.x tool from the PCM tools suite I get the following information (emphasis on number of QPI links):

Number of physical cores: 16
Number of logical cores: 32
Number of online logical cores: 32
Threads (logical cores) per physical core: 2
Num sockets: 2
Physical cores per socket: 8
Core PMU (perfmon) version: 3
Number of core PMU generic (programmable) counters: 4
Width of generic (programmable) counters: 48 bits
Number of core PMU fixed counters: 3
Width of fixed counters: 48 bits
Nominal core frequency: 2400000000 Hz
Package thermal spec power: 85 Watt; Package minimum power: 40 Watt; Package maximum power: 170 Watt; 
Socket 0: 2 memory controllers detected with total number of 5 channels. 2 QPI ports detected.
Socket 1: 2 memory controllers detected with total number of 5 channels. 2 QPI ports detected.
Trying to use Linux perf events...
Successfully programmed on-core PMU using Linux perf
Socket 0
Max QPI link 0 speed: 16.0 GBytes/second (8.0 GT/second)
Max QPI link 1 speed: 16.0 GBytes/second (8.0 GT/second)
Socket 1
Max QPI link 0 speed: 16.0 GBytes/second (8.0 GT/second)
Max QPI link 1 speed: 16.0 GBytes/second (8.0 GT/second)

A few natural questions that have risen:

  • Do I have 2 QPI links or 4 links?
  • What is the difference between the "socket" and the "QPI link" that the tool refers to?
  • Is the maximum transfer bandwidth of each socket 16 GB/sec or 32 GB/sec?
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    Looks like you have dual-CPU, i.e. you have two E5-2630 v3 CPUs installed. 2x 2 links = 4 links.
    – Bob
    Commented Jun 12, 2017 at 5:01

1 Answer 1

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If you look at the output you fill find that it's listing the following for each of your CPUs:

Max QPI link 0 speed: 16.0 GBytes/second (8.0 GT/second)
Max QPI link 1 speed: 16.0 GBytes/second (8.0 GT/second)

So each CPU has two links which would be your expectation. It's not unusual to start numbering items with 0. So QPI link 0 is the first link, QPI link 1 would be the second.

The socket is, well, the physical socket of your CPUs. Again you will find it starts numbering with 0 for the first one.

The maximum transfer rate is 16 for an individual QPI link. It would depend on what they're used for and how they're connected in order to get more out of it.

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  • Thank you very much, that clarifies things. Therefore, the max. throughput of the each socket would be, theoretically, 32 GB/sec, since there are 2 QPI links per socket, right?
    – Adama
    Commented Jun 12, 2017 at 17:48
  • Yes but I'm not sure what they would be used for. E.g. one might be connected to the south bridge and one used for communication between CPUs. I just remember that my old i7 920 also has QPI link and if I'm not mistaken it was/is used to connect the chipset.
    – Seth
    Commented Jun 12, 2017 at 19:06

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