✎ library:computing:xios_impi_troubles []

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====== NEMO-XIOS issues with Intel MPI ======

===== NEMO-XIOS @ MN3 =====

**Environment:** NEMO 3.6 stable, XIOS 1.0. This bug was documented using the following compilers and MPI libraries:

* Intel 13.0.1 & Intel MPI 4.1.3.049
  * Intel 16.0.1 & Intel MPI 5.1.2.150

The problem was reported when using default optimization flags as well as using -O3 optimization flag.

**Problem:** When using more than 1.920 MPI processes (120 MN3 nodes), during the XIOS initialization, the simulation was falling into a dead lock:

Some of the __NEMO clients__ remain stuck in client.cpp doing an MPI send:

<code>
MPI_Send(buff,buffer.count(),MPI_CHAR,serverLeader,1,CXios::globalComm) ;
</code>

__XIOS master server__ (first XIOS process), remains in CServer::listenContext(void) routine at server.cpp, trying to dispatch all the messages:

<code>
MPI_Iprobe(MPI_ANY_SOURCE,1,CXios::globalComm, &flag, &status) ;
</code>

**Actions taken:** Prints were placed into the code, before and after the mentioned call. It could be seen that some NEMO processes were waiting in the MPI barrier (synchronous send), while XIOS master server was looping to infinite, trying to get all the messages (the total number of messages should be equal to the number of clients, or NEMO processes).

The error could be reproduced in a [[/wiki/doku.php?id=library:computing:xios_impi_troubles_bench|small code]], in order to facilitate the debug and the error fixing.

**Diagnosis:** It seemed that some messages sent from the clients to the master server were lost, maybe because all of these messages were sent from all the nodes at the same time.

**Solution:** Our first workaround was to include a call to the __sleep function__ before de MPI_Send in the clients' code, to interleave the outcome messages and avoid flooding buffers and network. This obviously is not the cleanest solution, because it introduces a total delay of 15 secs. in the execution, but it is an affordable approach, given that this code is only executed in the initialization.

<code>
char hostName[50];
gethostname(hostName, 50);

// Sleep Fix
sleep(rank%16);

MPI_Comm_create_errhandler(eh, &newerr);
MPI_Comm_set_errhandler(CXios::globalComm, newerr );

error_code = MPI_Send(buff,buffer.count(),MPI_CHAR,serverLeader,1,CXios::globalComm) ;

delete [] buff ;
</code>

BSC operations provided another solution: enabling the __User Datagram__ protocol by using Intel's MPI environment variables (more information below). This alternative works and doesn't need any code modification, but it entails a penalty in performance: we observed that simulations using this option were increasingly slower (5%-20%) as the number of cores was aumented, in comparison with the reference ones.

**More information:**

This bug was reported in the XIOS portal:

[[http://forge.ipsl.jussieu.fr/ioserver/ticket/90]]

About Intel Communication Fabrics control:

[[https://software.intel.com/en-us/node/528821]]

DAPL UD-capable Network Fabrics Control:

[[https://software.intel.com/en-us/node/528824]]

===== NEMO-XIOS @ MN4 =====

==== Issue 1: ====

**Environment:** Auto-EC-Earth 3.2.2_develop_MN4 (EC-Earth 3.2 r4063-runtime-unification).

* Compiler: Intel 2017.4
  * MPI: Intel 2017.3.196
  * NetCDF: 4.4.4.1 & 4.2
  * HDF5: 1.8.19
  * Flags: -O3 & -O0

**Problem:** NEMO crashes in the initialization when reading input files:

__ocean.output__:

<code>
 ===>>> : E R R O R
         ===========

iom_nf90_check : NetCDF: Invalid argument
                     iom_nf90_open ~~~
                     iom_nf90_open ~~~ open existing file: ./weights_WOA13d1_2_o
 rca1_bilinear.nc in READ mode

===>>> : E R R O R
         ===========

iom_nf90_check : NetCDF: Invalid argument
                     iom_nf90_open ~~~

===>>> : E R R O R
         ===========

fld_weight : unable to read the file
                                                                                                                                                                                                                                                             879,6       Final
</code>

__log.err:__
<code>
forrtl: severe (408): fort: (7): Attempt to use pointer FLY_DTA when it is not associated with a target

Image              PC                Routine            Line        Source
nemo.exe           00000000027994F6  Unknown               Unknown  Unknown
nemo.exe           0000000000B3F219  fldread_mp_fld_in        1375  fldread.f90
nemo.exe           0000000000B15D4E  fldread_mp_fld_ge         614  fldread.f90
nemo.exe           0000000000B13A6B  fldread_mp_fld_in         413  fldread.f90
nemo.exe           0000000000B0A69B  fldread_mp_fld_re         175  fldread.f90
nemo.exe           0000000000978301  dtatsd_mp_dta_tsd         224  dtatsd.f90
nemo.exe           0000000000C312DF  istate_mp_istate_         196  istate.f90
nemo.exe           000000000043C33F  nemogcm_mp_nemo_i         326  nemogcm.f90
nemo.exe           000000000043A64D  nemogcm_mp_nemo_g         120  nemogcm.f90
nemo.exe           000000000043A606  MAIN__                     18  nemo.f90
nemo.exe           000000000043A5DE  Unknown               Unknown  Unknown
libc-2.22.so       00002B64D88596E5  __libc_start_main     Unknown  Unknown
nemo.exe           000000000043A4E9  Unknown               Unknown  Unknown
</code>

**Actions taken:** Operations had observed this error using NEMO standalone and NeTCDF 4.4.4.1, so they installed NetCDF 4.4.0 version. We could not reproduce the failure they reported with NEMO and NetCDF 4.4.4.1 but we got the same error when running EC-Earth. So we also moved to NetCDF 4.4.0. However, we got other XIOS errors when writing outputs (commented in following issues) and we asked for the same version we were using at MN3 to be installed. When operations installed 4.2 version we surprisingly got again the same error.

**Diagnosis:**

**Solution:**

**More information:**

This bug had already been reported in Unidata Github:

[[https://github.com/Unidata/netcdf4-python/issues/170|https://github.com/Unidata/netcdf4-python/issues/170]]

==== Issue 2: ====

**Environment:** Auto-EC-Earth 3.2.2_develop_MN4 (EC-Earth 3.2 r4063-runtime-unification).

* Compiler: Intel 2017.4
  * MPI: Intel 2017.3.196
  * NetCDF: 4.4.0
  * HDF5: 1.8.19
  * Flags: -O3 , with and without -fpe0

**Problem:** XIOS2 breaks when writing output files. As a result, output files are incomplete: they contain the headers for each one of the variables they are supposed to store, but only values for nav_lat, nav_lon, depthu and depthu_bounds are actually saved.

__ocean.output__: ocean.output looks normal, the stop is just after writing the restarts.

__log.err__:

<code>
forrtl: error (65): floating invalid
Image              PC                Routine            Line        Source
nemo.exe           0000000001B2B832  Unknown               Unknown  Unknown
libpthread-2.22.s  00002B2472B71B10  Unknown               Unknown  Unknown
nemo.exe           000000000189CE85  _ZN5blitz5ArrayId         182  fastiter.h
nemo.exe           000000000189BDE9  _ZN5blitz5ArrayId          89  methods.cc
nemo.exe           000000000189BA8C  _ZN4xios13COperat         175  operator_expr.hpp
nemo.exe           000000000188A3BA  _ZN4xios27CFieldF          61  binary_arithmetic_filter.cpp
nemo.exe           00000000018152E4  _ZN4xios7CFilter1          14  filter.cpp
nemo.exe           0000000001563FBE  _ZN4xios9CInputPi          37  input_pin.cpp
nemo.exe           000000000176284F  _ZN4xios10COutput          46  output_pin.cpp
nemo.exe           0000000001762A48  _ZN4xios10COutput          35  output_pin.cpp
nemo.exe           0000000001815364  _ZN4xios7CFilter1          16  filter.cpp
nemo.exe           0000000001563FBE  _ZN4xios9CInputPi          37  input_pin.cpp
nemo.exe           000000000176284F  _ZN4xios10COutput          46  output_pin.cpp
nemo.exe           0000000001762A48  _ZN4xios10COutput          35  output_pin.cpp
nemo.exe           0000000001815364  _ZN4xios7CFilter1          16  filter.cpp
nemo.exe           0000000001563FBE  _ZN4xios9CInputPi          37  input_pin.cpp
nemo.exe           000000000176284F  _ZN4xios10COutput          46  output_pin.cpp
nemo.exe           0000000001762A48  _ZN4xios10COutput          35  output_pin.cpp
nemo.exe           000000000178A260  _ZN4xios13CSource          32  source_filter.cpp
nemo.exe           0000000001812DC7  _ZN4xios6CField7s          21  field_impl.hpp
nemo.exe           00000000014B3586  cxios_write_data_         434  icdata.cpp
nemo.exe           0000000000FFE0FD  idata_mp_xios_sen         552  idata.F90
nemo.exe           0000000000738081  diawri_mp_dia_wri         252  diawri.f90
nemo.exe           0000000000485B67  step_mp_stp_              284  step.f90
nemo.exe           000000000043908B  nemogcm_mp_nemo_g         147  nemogcm.f90
nemo.exe           0000000000438FDD  MAIN__                     18  nemo.f90
nemo.exe           0000000000438F9E  Unknown               Unknown  Unknown
libc-2.22.so       00002B247309B6E5  __libc_start_main     Unknown  Unknown
nemo.exe           0000000000438EA9  Unknown               Unknown  Unknown
                                                                                                                                                                                                                                                             2517,1      Final
</code>

**Actions taken:** Given that the error is a floating invalid we disabled the -fpe0 flag, but we still were having the same problem. Then we disabled compiler optimizations (use -O0) and the problem disappeared, but this obviously has an effect on performance.

**Diagnosis:**

**Solution:** Disabling compiler optimizations (activate -O0).

==== Issue 3: ====

**Environment:**

**Problem:**

**Actions taken:**

**Diagnosis:**

**Solution:**

==== Issue 4: ====

**Environment:**

**Problem:**

**Actions taken:**

**Diagnosis:**

**Solution:**

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