How do I calculate the bandwidth of the PCIe sockets? Why are only 2 sockets listed?

[KevinLucidyne]

I'm working in deep learning and I'm trying to identify a bottleneck in our GPU pipeline.

We're running Ubuntu on an Intel Xeon motherboard with 4 NVIDIA Titan RTXs. Use of the GPUs seems to be pretty low even though the memory usage is around 97%.

So I'm trying to see if the bus is the bottleneck.

I've downloaded PCM and I'm running it to monitor the PCIe 3.0 x16 traffic.

Processor Counter Monitor: PCIe Bandwidth Monitoring Utility 
 This utility measures PCIe bandwidth in real-time

 PCIe event definitions (each event counts as a transfer): 
   PCIe read events (PCI devices reading from memory - application writes to disk/network/PCIe device):
     PCIeRdCur* - PCIe read current transfer (full cache line)
         On Haswell Server PCIeRdCur counts both full/partial cache lines
     RFO*      - Demand Data RFO
     CRd*      - Demand Code Read
     DRd       - Demand Data Read
   PCIe write events (PCI devices writing to memory - application reads from disk/network/PCIe device):
     ItoM      - PCIe write full cache line
     RFO       - PCIe partial Write
   CPU MMIO events (CPU reading/writing to PCIe devices):
     PRd       - MMIO Read [Haswell Server only] (Partial Cache Line)
     WiL       - MMIO Write (Full/Partial)
...
Socket 0: 2 memory controllers detected with total number of 6 channels. 3 QPI ports detected. 2 M2M (mesh to memory) blocks detected.
Socket 1: 2 memory controllers detected with total number of 6 channels. 3 QPI ports detected. 2 M2M (mesh to memory) blocks detected.
Trying to use Linux perf events...
Successfully programmed on-core PMU using Linux perf
Link 3 is disabled
Link 3 is disabled
Socket 0
Max QPI link 0 speed: 23.3 GBytes/second (10.4 GT/second)
Max QPI link 1 speed: 23.3 GBytes/second (10.4 GT/second)
Socket 1
Max QPI link 0 speed: 23.3 GBytes/second (10.4 GT/second)
Max QPI link 1 speed: 23.3 GBytes/second (10.4 GT/second)

Detected Intel(R) Xeon(R) Gold 5122 CPU @ 3.60GHz "Intel(r) microarchitecture codename Skylake-SP" stepping 4 microcode level 0x200004d
Update every 1.0 seconds
delay_ms: 54
Skt | PCIeRdCur |  RFO  |  CRd  |  DRd  |  ItoM  |  PRd  |  WiL
 0      13 K        19 K     0       0      220 K    84     588  
 1       0        3024       0       0        0       0     264  
-----------------------------------------------------------------------
 *      13 K        22 K     0       0      220 K    84     852  

Ignore the actual values for a moment. I have much bigger values. :-)

How do I calculate the bandwidth of the PCIe socket?

Why are there only two sockets listed?

[opcm]

socket refer to CPU sockets not PCIe slots or devices. You have a system with 2 CPU sockets, right?
The --help output describes -B switch to output bandwidth per CPU socket (see also caveat here with partial operations). pci-iio.x is a different utility that shows bandwidth per PCIe device.