Hi, Paul

I must say, this is eerily appropo. I've just sent a request for Wombat
last week as I was planning to have my group start looking at the
performance of UCX OSC on IB. We are most interested in ensuring UCX OSC MT
performs well on Wombat. The bitbucket you're referencing; is this the
source code? Can we build and run it?



On Fri, Aug 23, 2019 at 9:37 PM Paul Edmon via users <
users@lists.open-mpi.org> wrote:

> I forgot to include that we have not rebuilt this OpenMPI 4.0.1 against
> 1.6.0 of UCX but rather 1.5.1.  When we upgraded to 1.6.0 everything seemed
> to be working for OpenMPI when we swapped the UCX version with out
> recompiling (at least in normal rank level MPI as we had to do the upgrade
> to UCX to get MPI_THREAD_MULTIPLE to work at all).
> -Paul Edmon-
> On 8/23/2019 9:31 PM, Paul Edmon wrote:
> Sure.  The code I'm using is the latest version of Wombat (
> https://bitbucket.org/pmendygral/wombat-public/wiki/Home , I'm using an
> unreleased updated version as I know the devs).  I'm using
> OMP_THREAD_NUM=12 and the command line is:
> mpirun -np 16 --hostfile hosts ./wombat
> Where the host file lists 4 machines, so 4 ranks per machine and 12
> threads per rank.  Each node has 48 Intel Cascade Lake cores. I've also
> tried using the Slurm scheduler version which is:
> srun -n 16 -c 12 --mpi=pmix ./wombat
> Which also hangs.  It works if I constrain to one or two nodes but any
> greater than that hangs.  As for network hardware:
> [root@holy7c02101 ~]# ibstat
> CA 'mlx5_0'
>         CA type: MT4119
>         Number of ports: 1
>         Firmware version: 16.25.6000
>         Hardware version: 0
>         Node GUID: 0xb8599f0300158f20
>         System image GUID: 0xb8599f0300158f20
>         Port 1:
>                 State: Active
>                 Physical state: LinkUp
>                 Rate: 100
>                 Base lid: 808
>                 LMC: 1
>                 SM lid: 584
>                 Capability mask: 0x2651e848
>                 Port GUID: 0xb8599f0300158f20
>                 Link layer: InfiniBand
> [root@holy7c02101 ~]# lspci | grep Mellanox
> 58:00.0 Infiniband controller: Mellanox Technologies MT27800 Family
> [ConnectX-5]
> As for IB RDMA kernel stack we are using the default drivers that come
> with CentOS 7.6.1810 which is rdma core 17.2-3.
> I will note that I successfully ran an old version of Wombat on all 30,000
> cores of this system using OpenMPI 3.1.3 and regular IB Verbs with no
> problem earlier this week, though that was pure MPI ranks with no threads.
> Nonetheless the fabric itself is healthy and in good shape.  It seems to be
> this edge case using the latest OpenMPI with UCX and threads that is
> causing the hang ups.  To be sure the latest version of Wombat (as I
> believe the public version does as well) uses many of the state of the art
> MPI RMA direct calls, so its definitely pushing the envelope in ways our
> typical user base here will not.  Still it would be good to iron out this
> kink so if users do hit it we have a solution.  As noted UCX is very new to
> us and thus it is entirely possible that we are missing something in its
> interaction with OpenMPI.  Our MPI is compiled thusly:
> https://github.com/fasrc/helmod/blob/master/rpmbuild/SPECS/centos7/openmpi-4.0.1-fasrc01.spec
> I will note that when I built this it was built using the default version
> of UCX that comes with EPEL (1.5.1).  We only built 1.6.0 as the version
> provided by EPEL did not build with MT enabled, which to me seems strange
> as I don't see any reason not to build with MT enabled.  Anyways that's the
> deeper context.
> -Paul Edmon-
> On 8/23/2019 5:49 PM, Joshua Ladd via users wrote:
> Paul,
> Can you provide a repro and command line, please. Also, what network
> hardware are you using?
> Josh
> On Fri, Aug 23, 2019 at 3:35 PM Paul Edmon via users <
> users@lists.open-mpi.org> wrote:
>> I have a code using MPI_THREAD_MULTIPLE along with MPI-RMA that I'm
>> using OpenMPI 4.0.1.  Since 4.0.1 requires UCX I have it installed with
>> MT on (1.6.0 build).  The thing is that the code keeps stalling out when
>> I go above a couple of nodes.  UCX is new to our environment as
>> previously we have just used the regular IB Verbs with no problem.  My
>> guess is that there is either some option in OpenMPI I am missing or
>> some variable in UCX I am not setting.  Any insight on what could be
>> causing the stalls?
>> -Paul Edmon-
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