# Change CPU frequency on ARCHER2

**URL:** <https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864>\
**Category:** Unified Model\
**Tags:** ARCHER2\
**Created:** [16 January 2023 14:54 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864 "2023-01-16T14:54:53Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![sebsteinig](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@sebsteinig](https://cms-helpdesk.ncas.ac.uk/u/sebsteinig)\
**Post date:** [16 January 2023 14:54 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864/1 "2023-01-16T14:54:53Z")

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Hi,

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](https://docs.archer2.ac.uk/user-guide/energy/)) 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,  
Seb

* * *

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.

**09/11/2022:**  
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

**13/01/2023**  
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.

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<div class="post-metadata">

**Author:** ![dcase](https://dub1.discourse-cdn.com/flex013/user_avatar/cms-helpdesk.ncas.ac.uk/dcase/32/468_2.png) [@dcase](https://cms-helpdesk.ncas.ac.uk/u/dcase)\
**Post date:** [16 January 2023 15:18 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864/2 "2023-01-16T15:18:53Z")

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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.

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**Author:** ![grenville](https://dub1.discourse-cdn.com/flex013/user_avatar/cms-helpdesk.ncas.ac.uk/grenville/32/29_2.png) [@grenville](https://cms-helpdesk.ncas.ac.uk/u/grenville)\
**Post date:** [16 January 2023 15:36 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864/3 "2023-01-16T15:36:51Z")

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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`

under  
[[HPC]]  
…  
[[[environment]]]  
SLURM\_CPU\_FREQ\_REQ=2250000

that will then get exported by cylc.

Grenville

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<div class="post-metadata">

**Author:** ![sebsteinig](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@sebsteinig](https://cms-helpdesk.ncas.ac.uk/u/sebsteinig)\
**Post date:** [16 January 2023 20:00 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864/4 "2023-01-16T20:00:38Z")

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

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**Author:** ![system](https://europe1.discourse-cdn.com/flex013/uploads/cms_support/original/1X/1fd2411499ffcbc299fe756cd5cdf26e44956558.png) [@system](https://cms-helpdesk.ncas.ac.uk/u/system)\
**Post date:** [18 January 2023 20:00 UTC](https://cms-helpdesk.ncas.ac.uk/t/change-cpu-frequency-on-archer2/864/5 "2023-01-18T20:00:39Z")

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