Changes between Version 1 and Version 2 of ticket/1721/General

Timestamp:

2016-04-29T10:38:10+02:00 (8 years ago)

Author:

frrh

Comment:

--

ticket/1721/General

@@ -1 +1 @@
 
 == Running eORCA1 on a single Cray XC40 PE ==
+
+
+=== Background notes ===
+Higher resolutions (e.g. eORCA025) cannot run on a single node so we concentrate solely on eORCA1 for the purposes of this work.
+
+Tim Graham has run a gyre ORCA2 configuration successfully on a single PE.
+
+Here we aim to go up a level. 
+
+=== Procedures and observations ===
+
+
+It turns out that if we take an eORCA1 NEMO-CICE GO6-type configuration and employ 1x1 with no separate XIOS server PEs then the 
+job fails with a very clear message from icbinit (iceberg initialisation) that it is not possible to run with 1 PE in the X direction.... 
+
+Note: we have to manually adjust the aprun command line options to get what we need because the logic in the existing 
+controls (in suite.rc) breaks down when running on 1x1 (and possibly all odd numbers) of PEs. 
+
+
+The reasons for that are not clear (why would iceberg code be any different from the main NEMO (or CICE) code. That seems odd but I don't 
+propose to pursue it.
+
+So try switching off icebergs....
+
+Well this seems to submit and start running but times out with no suggestion that it has got very far (no time.step file etc). It's not 
+clear if things are failing somewhere in the NEMO code, in CICE or in the IO.  
+
+
+Try extending the run time and shortening the total run to 6 hours... 
+
+
+This seems to abort in XIOS with an allocation problem.
+
+How about we add separate XIOS procs back to the job?
+
+Setting up to run with 8 separate XIOS processes in detached mode... that fails too. 
+
+It seems that regardless of how long we give the model to run, it reads (at least some of) the NEMO namelists and then just hangs. 
+
+Tim says this smacks of an XIOS problem. 
+
+He suggests switching off XIOS (in the external libraries control of fcm_make_ocean) and deactivating key_iomput. 
+
+So I do this and set the run to go for 6 hours (8x45 min TS in this case.)
+
+This actually seems to work and sure enough at the end of the run we have a single NEMO restart file for the whole domain. 
+
+So it seems we can run eORCA1 on a single PE with the caveats that:
+
+   * we must turn off icebergs
+   * we must not compile with key_iomput
+   * we must turn off XIOS completely from the compilation (i.e. not merely leave it to run in attached mode).
+
+So not exactly an unqualified success but better than we might have hoped and potentially giving us something 
+to work with should we need it.   
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