[ofa-general] PCI-Express payload

[Dotan Barak]

Hi.

You can check what is the maximum supported MTU of your HCA using 
ibv_devinfo.
Most of the HCAs supports 2KB MTU and some of them 4KB MTU.

The MTU is the maximum payload size that can be sent/received
(the space for the IB headers are not part of the MTU)


Every connected QP (RC/UC) can define which MTU value he is using 
(according to the
used path).


I hope that is the info you asked for ..
Dotan

Koen Segers wrote:
> Hi,
>
> I'm interested in computing the overhead coming from PCI-Express to an 
> IB HCA. Therefore I need to know the payload size of different types 
> of HCA.
>
> We have InfiniHost III Mellanox cards of 4x SDR and DDR IB. According 
> the lspci -vvv command on SLES 10 SP1, the PCI-e payload of these 
> cards is maximum 128 bytes.
>
> Can someone give my the payload size for a ConnectX 4x SDR and DDR IB 
> card?
>
> Thank you,
>
> Koen
>
> This is my output:
> 41:00.0 InfiniBand: Mellanox Technologies MT25208 InfiniHost III Ex 
> (rev a0)
>         Subsystem: Mellanox Technologies MT25208 InfiniHost III Ex
>         Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- 
> ParErr+ Stepping- SERR- FastB2B-
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- 
> <TAbort- <MAbort- >SERR- <PERR-
>         Latency: 0, Cache Line Size: 64 bytes
>         Interrupt: pin A routed to IRQ 209
>         Region 0: Memory at e1700000 (64-bit, non-prefetchable) [size=1M]
>         Region 2: Memory at e1800000 (64-bit, prefetchable) [size=8M]
>         Capabilities: [40] Power Management version 2
>                 Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA 
> PME(D0-,D1-,D2-,D3hot-,D3cold-)
>                 Status: D0 PME-Enable- DSel=0 DScale=0 PME-
>         Capabilities: [48] Vital Product Data
>         Capabilities: [90] Message Signalled Interrupts: Mask- 64bit+ 
> Queue=0/5 Enable-
>                 Address: 0000000000000000  Data: 0000
>         Capabilities: [84] MSI-X: Enable+ Mask- TabSize=32
>                 Vector table: BAR=0 offset=00082000
>                 PBA: BAR=0 offset=00082200
>         Capabilities: [60] Express Endpoint IRQ 0
> *                Device: Supported: MaxPayload 128 bytes, PhantFunc 0, 
> ExtTag+*
>                 Device: Latency L0s <64ns, L1 unlimited
>                 Device: AtnBtn- AtnInd- PwrInd-
>                 Device: Errors: Correctable- Non-Fatal+ Fatal+ 
> Unsupported-
>                 Device: RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
>                 Device: MaxPayload 128 bytes, MaxReadReq 4096 bytes
>                 Link: Supported Speed 2.5Gb/s, Width x8, ASPM L0s, Port 8
>                 Link: Latency L0s unlimited, L1 unlimited
>                 Link: ASPM Disabled RCB 128 bytes CommClk- ExtSynch-
>                 Link: Speed 2.5Gb/s, Width x8
>
>  
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