[ofa-general] Configuring a 4 KB InfniBand link MTU

[James Lentini]

On Wed, 7 Jan 2009, Hal Rosenstock wrote:

<snip>
> If the switch ports support a 4K MTU cap, it needs to be advertised 
> (via the PortInfo response). That's what needs fixing if possible 
> rather than some SM policy. Without an MTUCap of 4K on both sides of 
> the link, an SM cannot set NeighborMTU to 4K.

Thanks Hal. I'll do some more research on my switch to see if it is 
indeed capable of a 4 KB MTU.

This datasheet on the MT47396 lists a 4 KB MTU as one of its features:

 http://www.mellanox.com/related-docs/prod_silicon/InfiniScaleIII.pdf

Perhaps the version of the chip I have doesn't support a 4 KB MTU or 
the switch hardware/firmware doesn't support it.

> > # smpquery portinfo 2 1
> > # Port info: Lid 2 port 1
> > Mkey:............................0x0000000000000000
> > GidPrefix:.......................0x0000000000000000
> > Lid:.............................0x0000
> > SMLid:...........................0x0000
> > CapMask:.........................0x0
> > DiagCode:........................0x0000
> > MkeyLeasePeriod:.................0
> > LocalPort:.......................1
> > LinkWidthEnabled:................4X
> > LinkWidthSupported:..............1X or 4X
> > LinkWidthActive:.................4X
> > LinkSpeedSupported:..............2.5 Gbps or 5.0 Gbps
> > LinkState:.......................Active
> > PhysLinkState:...................LinkUp
> > LinkDownDefState:................Polling
> > ProtectBits:.....................0
> > LMC:.............................0
> > LinkSpeedActive:.................5.0 Gbps
> > LinkSpeedEnabled:................2.5 Gbps or 5.0 Gbps
> > NeighborMTU:.....................2048
> > SMSL:............................0
> > VLCap:...........................VL0-7
> > InitType:........................0x00
> > VLHighLimit:.....................0
> > VLArbHighCap:....................8
> > VLArbLowCap:.....................8
> > InitReply:.......................0x00
> > MtuCap:..........................2048
> > VLStallCount:....................7
> > HoqLife:.........................18
> > OperVLs:.........................VL0-7
> > PartEnforceInb:..................0
> > PartEnforceOutb:.................0
> > FilterRawInb:....................0
> > FilterRawOutb:...................0
> > MkeyViolations:..................0
> > PkeyViolations:..................0
> > QkeyViolations:..................0
> > GuidCap:.........................0
> > ClientReregister:................0
> > SubnetTimeout:...................0
> > RespTimeVal:.....................0
> > LocalPhysErr:....................15
> > OverrunErr:......................15
> > MaxCreditHint:...................0
> > RoundTrip:.......................0
> >
> > and I confirmed that the switch had a MT47396:
> >
> > # smpquery nodeinfo 2
> > # Node info: Lid 2
> > BaseVers:........................1
> > ClassVers:.......................1
> > NodeType:........................Switch
> > NumPorts:........................24
> > SystemGuid:......................0x0005ad03011df356
> > Guid:............................0x0005ad00001df356
> > PortGuid:........................0x0005ad00001df356
> > PartCap:.........................8
> > DevId:...........................0xb924
> > Revision:........................0x000001a1
> > LocalPort:.......................1
> > VendorId:........................0x0005ad
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