Diagnostic frequency

[Denis Sergeev (dennissergeev)]

What is the correct way to specify the frequency of output in LFRic and GungHo?

There is diagnostic_frequency in the .conf files but there is also various frequency parameters in the XML files - so I'm confused what combination of those I should use (I'm also getting a SEGFAULT during output).

[Steve Mullerworth (stevemullerworth)]

The correct way for most diagnostics coming out of the science code would be to select the frequency in your XML file. The logic in the model should check with XIOS before computing such diagnostics and sending them to XIOS.

The diagnostic_frequency setting relates largely to a set of diagnostics output at the end of each time-step (see gungho_diagnostics_driver_mod). These were added early in the development of the model. It was decided that it would be easier to set a frequency in the XML so that XIOS expects them every time-step, but to use model logic to control the actual output frequency. This is because we can control the frequency through the namelist whereas modifying the XML would be fiddly.

The diagnostics output from the science algorithms (as opposed to gungho_diagnostics_driver_mod) should be controllable by the XML file. Model logic will check with XIOS before computing such diagnostics and sending them to XIOS. (There appears to be a small number of diagnostics output by science algorithms that are also controlled by diagnostic_frequency - I think this is an error.)

Setting write_diag=.false. should prevent any diagnostics being written.

[Denis Sergeev (dennissergeev)]

Thanks Steve Mullerworth (@stevemullerworth)! I still can't quite wrap my head around why different optional configurations in the rose-stem suite (especially for gungho_model) have different diagnostic_frequency. Is it because otherwise one would need a separate XML file for every test?

For example, for io_clim, diagnostic_frequency is set to 48 but in the corresponding file_def_diags_climate.xml, the freq_op parameter is set to every time step. So what is the sampling frequency in this case? Why isn't the diagnostic_frequency set to 1 in rose-app-io_clim.conf?

[Steve Mullerworth (stevemullerworth)]

Either we would need a separate XML file for each test (with a different frequency option) or we somehow set or override the frequency option depending on the configuration. The latter should be supported by XIOS, but the basic system was written several years ago when the capabilities of XIOS were less clear.

In the io_clim task, the sampling frequency for the diagnostics in gungho_diagnostics_driver_mod would be every 48 timesteps. Setting diagnostic_frequency to 1 would mean much more (wasted) output. Setting freq_op to 48, on the other hand, would be a pain if you want to do a quick 1 timestep test of the app because you've found a bug (it's practically easier to change the diagnostic frequency in the configuration file).

Now things have moved on, we ought to retire the ability to control output using diagnostic frequency, but there would be quite a bit of work to do to support the current usage.

[Denis Sergeev (dennissergeev)]

OK, I see! Many thanks Steve Mullerworth (@stevemullerworth)!

[iboutle]

Not much to add to this really - the preferred method is definitely to set "diagnostic_frequency=1" (this simply allows diagnostic calculations to be done on every timestep), and use the appropriate settings in the xml files to control when you want the diagnostics calculated and output. For any standalone suites or real science this is definitely the method that should be used.

In gungho_model, diagnostic_frequency is still used to avoid having to duplicate the xml files for every different output frequency that is wanted by the test suite. It's quite dangerous however because it's essentially restricting when xios is given data, so is prone to segfaults if xios is trying to do something with data it has not been given.

[Denis Sergeev (dennissergeev)]

Thanks iboutle!!