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entstat -d entXX : What is the meaning of "PCIe Link Speed" ?

  • 1.  entstat -d entXX : What is the meaning of "PCIe Link Speed" ?

    Posted Mon July 01, 2013 11:11 AM

    Originally posted by: LaurentOliva


    By using "entstat" of my 10Gbps NICs, I'd like to know what is the exact meaning of the "PCIe Link Speed" field ?

    I have the following 10Gbps NICs :

    ent0:a2191007d003000:PCIe2 2-port 10GbE SR Adapter (a21910071410d003)
    ent1:a2191007d003000:PCIe2 2-port 10GbE SR Adapter (a21910071410d003)
    ent2:a2191007d003000:PCIe2 2-port 10GbE SR Adapter (a21910071410d003)
    ent3:a2191007d003000:PCIe2 2-port 10GbE SR Adapter (a21910071410d003)
     

    Those are wired to 10Gbps switches :

    ...

    PCIe2 2-port 10GbE SR Adapter (a21910071410d003) Specific Statistics:
    ---------------------------------------------------------------------
    Link Status: Up
    Media Speed Running: 10 Gbps Full Duplex
    PCI Mode: PCI-Express X8
            Relaxed Ordering: Disabled
            TLP Size: 512
            MRR Size: 4096
            PCIe Link Speed: 5.0 Gbps
    Jumbo Frames: Disabled
    Transmit TCP segmentation offload: Enabled
    Receive TCP segment aggregation: Enabled
     

    By reading the entstat ouput, it seems that the PCIe bus is limited to 5Gbps, which is exactly half of a card capability !

    Server type is : 9117-MMC

    Cards are installed onto a CEC which have PCIe Gen2 ports.

    By reading specs from redbook or world wide internet ressources, those slots should normally handle up to 4GB/s !! (500MB/s per lane)

    What i misunderstand ?

    My bandwith bench tends to confirm the bus speed....

    thanks

     

     

     

     



  • 2.  Re: entstat -d entXX : What is the meaning of "PCIe Link Speed" ?

    Posted Tue July 09, 2013 10:27 AM

    Originally posted by: LaurentOliva


    The 5Gbps "link speed" is the PCI-e throughput per "lane" to the PCI bus;  
and the "x8" shows the slot is an 8 lane slot for the PCI card; 

so the theoretical maximum throughput for the slot data transfer is 8 times 5Gbps which is 40 Gbps.