[OMPI users] UCX and MPI_THREAD_MULTIPLE

[Paul Edmon via users]

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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Re: [OMPI users] UCX and MPI_THREAD_MULTIPLE

[Jeffrey Layton via users]

Adding the UCX list to this thread.


On Fri, Aug 23, 2019 at 7:35 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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> users@lists.open-mpi.org
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Re: [OMPI users] UCX and MPI_THREAD_MULTIPLE

[Joshua Ladd via users]

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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> users mailing list
> users@lists.open-mpi.org
> https://lists.open-mpi.org/mailman/listinfo/users
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Re: [OMPI users] UCX and MPI_THREAD_MULTIPLE

[Paul Edmon via users]

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 
mailto: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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Re: [OMPI users] UCX and MPI_THREAD_MULTIPLE

[Paul Edmon via users]

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 
mailto: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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