ok Thx for all your explanations. So the MTU value which I'm seeing on the ib0 interface (65520) is not connected to the "real" infiniband MTU value ?
Le 07/12/2010 16:52, Mike Heinz a écrit : > Heh. I forgot Intel sells an mpi, I thought you were saying you had > recompiled one of the OFED mpis with icc. > > 1) For your small cluster, there's no reason not to use connected mode. The > only reason for providing a datagram mode with MPI is to support very large > clusters where there simply aren't enough system resources for every node to > connect with every other node. > > I would still suggest experimenting with mvapich-1 (and recompiling it with > icc) to see if you get better performance. > > 2) Similarly, for a small cluster, QoS won't give you any benefit. The > purpose of QoS is to divide up the fabric's bandwidth so that multiple > simultaneous apps can share it in a controlled way. If you're only running > one app at a time (which seems likely) you want that app to get all available > bandwidth. > > I'm not sure how you check the MTU size when using stock OFED, but my memory > for those HCAs is that they can use 2k MTUs. You only use a smaller MTU size > when the larger size causes reliability problems. > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf > Of giggzounet > Sent: Tuesday, December 07, 2010 10:32 AM > To: [email protected] > Subject: Re: [ewg] Need help for Infiniband optimisation for our cluster > (MTU...) > > Hi, > > Thx for your answer! > > Particularly the explication between connected and datagram mode (I see > that with the IMB1 benchmarks of mpi)! > > The hardware we are using in details: > - on the master: Mellanox MHGH18-XTC ConnectX with VPI adapter, single > port 20Gb/s, PCIe2.0 x8 2.5GT/s > - on the nodes: Integrated Mellanox DDR Infiniband 20Gbs ConnectX with > QSFP Connector. > > How can I know the limit of the MTU size ? > > > On the Infiniband we are just using mpi with different CFD programs. But > always with mpi (intel mpi or openmpi). Sould I use QoS ? > > Thx for your help! > > > Le 07/12/2010 16:09, Richard Croucher a écrit : >> Connected mode will provide more throughput but datagram mode will provide >> lower latency. >> You don't say what HCA's you are using. Some of the optimizations for >> Connected mode are only available for the newer ConnectX QDR HCA's. >> >> Your HCA will probably limit the MTU size. Leave this as large as possible. >> >> If you are only running a single application on the InfiniBand you need not >> bother with QoS. If you are running multiple, then you do need to set >> this. This is quite complex since you need to define V'L's, their >> arbitration policies and assign SL's to them. This is described in the >> OpenSM docs. This is relevant even if you are using the embedded SM in the >> switch. >> >> AS a newbie, take a look in the ../OFED/docs >> There is probably all you need there. Mellanox also have some useful docs on >> their website. >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of giggzounet >> Sent: 07 December 2010 14:01 >> To: [email protected] >> Subject: [ewg] Need help for Infiniband optimisation for our cluster >> (MTU...) >> >> Hi, >> >> I'm new on this list. We have in our laboratory a little cluster: >> - master 8 cores >> - 8 nodes with 12 cores >> - DDR infiniband switch Mellanox MTS3600R >> >> On these machines we have an oscar cluster with CentOS 5.5. We have >> installed the ofed packages 1.5.1. The default config for the infiniband >> is used. So infiniband is running in connected mode. >> >> Our cluster is used to solve CFD (Computational Fluid Dynamics) >> problems. And I'm trying to optimize the infiniband network and so I >> have several questions: >> >> - Is it the right mailing list to ask ? (if not...where should I post ?) >> >> - Is there a how-to on infiniband optimisation ? >> >> - CFD computations need a lot of bandwidth. There are a lot of data >> exchange through MPI (we are using intel mpi). Has the infiniband mode >> (connected or datagram) influence in this case ? What is the "best" MTU >> for those computation ? >> >> >> Best regards, >> Guillaume >> >> _______________________________________________ >> ewg mailing list >> [email protected] >> http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg > > > _______________________________________________ > ewg mailing list > [email protected] > http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg _______________________________________________ ewg mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/ewg
