Change CPU frequency on ARCHER2


I noticed that the runtime of my UM suites (GC3.1/UM10.7) increased this month by about 25% compared to running the same suites in November of last year (see output at bottom). I was wondering whether this could be related to the CPU frequency on ARCHER2 that was reduced from 2.25 to 2.0 GHz on 12 Dec 2022?

I want to increase the CPU frequency again to test whether this is indeed the problem. The ARCHER2 documentation (Energy use - ARCHER2 User Documentation) recommends to add

‘export SLURM_CPU_FREQ_REQ=2250000’

to the job submission script. Could you point me to where I could add/change this in my UM suite (u-cn504)?

Thank you very much for your help.

Best regards,

Below is the information of two jobs (via ‘sacct’), each running one year of the same suite (u-cn504) with the same number of nodes.

JobID Elapsed ReqCPUFreq AllocNodes ConsumedEnergy

2583538 03:59:42 Unknown 8 55.65M
2583538.bat+ 03:59:42 0 1 7.44M
2583538.ext+ 03:59:42 0 8 55.65M
2583538.0+0 03:58:55 Unknown 6 14.89M
2583538.0+1 03:58:55 Unknown 1 7.34M
2583538.0+2 03:58:55 Unknown 1 3.72M

JobID Elapsed ReqCPUFreq AllocNodes ConsumedEnergy

2897996 04:56:37 Unknown 8 50.41M
2897996.bat+ 04:56:37 0 1 6.66M
2897996.ext+ 04:56:37 0 8 50.41M
2897996.0+0 04:55:07 2G 6 6.59M
2897996.0+1 04:55:06 2G 1 6.73M
2897996.0+2 04:55:06 2G 1 4.31M

The more recent jobs takes ~1 hour longer, but still consumes less energy due to the lower CPU frequency. But I want to reduce the runtime again.

I think that in site/archer2.rc there is a section [[HPC]] with a pre-script
If you add it in the prescript, I think it should work as you’ll use srun to launch the executable. I would give this a go and see.

Hi Seb

We too have noticed a degradation in performance with the change of clock speed. We’ll probably make a global change to revert to “fast”, but in the mean time, you can add in /home/wb19586/roses/u-cn504/site/archer2.rc



that will then get exported by cylc.


Thank you both for the replies - this worked and reduced the runtime by ~25% again!

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