[openib-general] Multi-port HCA

[john t]

Hi Shannon,

The bandwidth figures that you quoted below match with my readings for
single port Mellanox DDR HCA (both for unidirection and bidirection). So it
seems dual port SDR HCA performs as good as single port DDR HCA. It would
help if you can also tell the bandwidth that you got using one port of your
dual-port SDR HCA card. Was it half the bandwidth that you stated below,
which means having two SDR ports per HCA helps.

In my case it seems having two ports (DDR) per HCA does not increase BW,
since PCI-e x8 limit is 16 Gb/sec per direction and each of the two HCA
ports (DDR) though capable of transferring 16 Gb/sec in each direction, when
used together can not go above 16 Gb/sec.

Regards,
John T.


On 10/5/06, Shannon V. Davidson <svdavidson at charter.net> wrote:
>
> John,
>
> In our testing with dual port Mellanox SDR HCAs, we found that not all
> PCI-express implementations are equal.  Depending on the PCIe chipset, we
> measured unidirectional SDR dual-rail bandwidth ranging from 1100-1500
> MB/sec and bidirectional SDR dual-rail bandwidth ranging from 1570-2600
> MB/sec.  YMMV, but had good luck with Intel and Nvidia chipsets, and less
> success with the Broadcom Serverworks HT-1000 and HT-2000 chipsets. My last
> report (in June 2006) was that Broadcom was working to improve their
> PCI-express performance.
>
> Regards,
> Shannon
>
> john t wrote:
>
>  Hi Bernard,
>
> I had a configuration issue. I fixed it and now I get same BW (i.e. around
> 10 Gb/sec) on each port provided I use ports on different HCA cards. If I
> use two ports of the same HCA card then BW gets divided between these two
> ports. I am using Mellanox HCA cards and doing simple send/recv using
> uverbs.
>
> Do you think it could be an issue with Mallanox driver or could it be due
> to system/PCI-E limitation.
>
> Regards,
> John T.
>
>
> On 10/3/06, Bernard King-Smith <wombat2 at us.ibm.com > wrote:
> >
> >
> > John,
> >
> > Who's adapter (manufacturer) are you using? It is usually an adapter
> > implementation or driver issue that occures when you cannot scale across
> > multiple links. The fact that you don't scale up from one link, but it
> > appears they share a fixed bandwidth across N links means that there is a
> > driver or stack issue. At one time I think that IPoIB and maybe other IB
> > drivers used only one event queue across multiple links which would be a
> > bottleneck. We added code in the IBM EHCA driver to get round this
> > bottleneck.
> >
> > Are your measurements using MPI or IP. Are you using separate
> > tasks/sockets per link and using different subnets if using IP?
> >
> > Bernie King-Smith
> > IBM Corporation
> > Server Group
> > Cluster System Performance
> > wombat2 at us.ibm.com    (845)433-8483
> > Tie. 293-8483 or wombat2 on NOTES
> >
> > "We are not responsible for the world we are born into, only for the
> > world we leave when we die.
> > So we have to accept what has gone before us and work to change the only
> > thing we can,
> > -- The Future." William Shatner
> >
> > john t" < johnt1johnt2 at gmail.com> wrote on 10/03/2006 09:42:24 AM:
> > >
> > > Hi,
> > >
> > > I have two HCA cards, each having two ports and each connected to a
> > > separate PCI-E x8 slot.
> > >
> > > Using one HCA port I get end to end BW of 11.6 Gb/sec (uni-direction
> > RDMA).
> > > If I use two ports of the same HCA or different HCA, I get between 5
> > > to 6.5 Gb/sec point-to-point BW on each port. BW on each port
> > > further reduces if I use more ports. I am not able to understand
> > > this behaviour. Is there any limitation on max. BW that a system can
> > > provide? Does the available BW get divided among multiple HCA ports
> > > (which means having multiple ports will not increase the BW)?
> > >
> > >
> > > Regards,
> > > John T
> >
>
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> --
> ____________________________________________
>
> Shannon V. Davidson <svdavidson at charter.net> <svdavidson at charter.net>
> Senior Software Engineer            Raytheon
> 636-479-7465 office         443-383-0331 fax
> ____________________________________________
>
>
>
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