Topic
1 reply Latest Post - ‏2013-07-09T14:27:10Z by daboule
daboule
daboule
17 Posts
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Pinned topic entstat -d entXX : What is the meaning of "PCIe Link Speed" ?

‏2013-07-01T15:10:36Z |

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

 

 

 

 

  • daboule
    daboule
    17 Posts
    ACCEPTED ANSWER

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

    ‏2013-07-09T14:27:10Z  in response to daboule
    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.