Message boards : Number crunching : How can I change the number of CPU used by LHC
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Thund3rb1rd

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Message 35503 - Posted: 13 Jun 2018, 6:01:38 UTC

Is there a way to change the number of CPU used by LHC after the job has already been downloaded but before the job starts running? I've had nothing but trouble getting projects that use VM to play nicely together and have decided to download one job at a time for one project at a time and strictly limit the resources used.
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computezrmle
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Message 35504 - Posted: 13 Jun 2018, 6:27:19 UTC - in response to Message 35503.  

LHC's vbox WUs use 1 core, except ATLAS.
To limit ATLAS to 1 core set the project's web preferences to max # CPUs = 1:
https://lhcathome.cern.ch/lhcathome/prefs.php?subset=project

As some ATLAS batches need more RAM than it is defined by default settings, you may also use this app_config.xml
<app_config>
  <app>
    <name>ATLAS</name>
    <max_concurrent>1</max_concurrent>
  </app>
  <app_version>
    <app_name>ATLAS</app_name>
    <plan_class>vbox64_mt_mcore_atlas</plan_class>
    <avg_ncpus>1.0</avg_ncpus>
    <cmdline>--nthreads 1 --memory_size_mb 4800</cmdline>
  </app_version>
</app_config>
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Crystal Pellet
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Message 35508 - Posted: 13 Jun 2018, 12:50:30 UTC

After adjustments in the app_config.xml, you have to 'Read config files' from the Options menu in BOINC Manager, before starting the new jobs.
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Toby Broom
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Message 35517 - Posted: 13 Jun 2018, 18:22:02 UTC

It should be possible via the web configurations, probably Max # CPU = 1 (you might have to set jobs too)
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Thund3rb1rd

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Message 35520 - Posted: 14 Jun 2018, 5:08:13 UTC

First - not to forget my manners - many thanks to those of you who took a moment to give me a hand. I genuinely appreciate your help.

I cut-and-pasted the app_config file provide by computezrmle into notepad.exe and created a file I named app_config.xml in the lhcathome.cern.ch_lhcathome directory.

I then returned to BOINC Manager, selected the lhc@home project, and invoked 'Read config files' from the BOINC Manager Options menu.

I immediately received this error message in the Notices tab:
LHC@home: Notice from BOINC
Missing <app_config> in app_config.xml

The <app_config> phrase shows quite clearly as the very first line in the app_config file I created. So - what did I do wrong?
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computezrmle
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Message 35521 - Posted: 14 Jun 2018, 5:17:03 UTC - in response to Message 35520.  

Check if you copy-pasted the first "<" and add a blank line at the end of the file.
Then reload it again.
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Alessio Susi
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Message 35746 - Posted: 2 Jul 2018, 13:23:22 UTC

One of my "Theory Simulations" tasks have used 15 cores (I have a Ryzen 7 1700, 8 cores 16 threads set to do 15 tasks simultaneously).
How can I set Theory tasks to use only 1 core?
ASUS X570 E-Gaming
AMD Ryzen 9 3950X, 16 core / 32 thread 4.4 GHz
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Erich56

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Message 35747 - Posted: 2 Jul 2018, 13:49:00 UTC - in response to Message 35746.  

On your Preferences page, simply set

Max # CPUs to "1"

then click on the "Update" button right underneath, and also in the BOINC Manager -> Projects -> LHC click on the "Update" button. So, only 1 CPU core will be used, for all tasks you download from then on.
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Message boards : Number crunching : How can I change the number of CPU used by LHC


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