I notice in the above file it is possible to get BOINC to lie about how many cores it has to projects. I did play with doubling this from 2 to 4 and one of the four tasks crashed.

Out of interest, has anyone else tried playing with this?

Yes, kid, you can, and I have, played with the various BOINC algorhythms. :) and how.

BUT -- I say BUT

Complain to BOINC -- not here??
Maybe there's another forum about hacking BOINC.
I'm thinking not rerlevant to CPDN

I notice in the above file it is possible to get BOINC to lie about how many cores it has to projects. I did play with doubling this from 2 to 4 and one of the four tasks crashed.

Out of interest, has anyone else tried playing with this?

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I have played with most of the cc_config.xml options and even helped some get added as features.
There isn't really any benefit to running more tasks than you have processors. Other than avoiding the time amount of time it takes between one task stopping and a new one starting.
It may gain you about 0.00005% in processing if the apps don't crash.

From the BOINC client configuration wiki. See https://boinc.berkeley.edu/wiki/Client_configuration

<ncpus>N</ncpus>
Act as if there were N CPUs; e.g. to simulate 2 CPUs on a machine that has only 1. To use the number of available CPUs, set the value to -1 (was 0 which in newer clients really means zero).

There is no reason for you to use it. If you want to reduce the number of cores available to BOINC the recommended way is to set the percentage of available CPU's to a value less than 100%. Setting to to a value higher than the number of cores/threads on your computer will force it to swap things in and out and your machine performance will suffer.

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BOINC blog

There is no reason for you to use it. If you want to reduce the number of cores available to BOINC the recommended way is to set the percentage of available CPU's to a value less than 100%

Though you can use it to limit the number of cores/project

e.g. <project_max_concurrent>1</project_max_concurrent>
</app_config>

Useful if you are running a project that requires virtualbox. On this machine if I don't make sure one core isn't running vitual box it makes it unusable at times. Also useful for those who want to micromanage different projects without having to play about with share ratios.

Though you can use it to limit the number of cores/project

e.g. <project_max_concurrent>1</project_max_concurrent>
</app_config>

Useful if you are running a project that requires virtualbox. On this machine if I don't make sure one core isn't running vitual box it makes it unusable at times. Also useful for those who want to micromanage different projects without having to play about with share ratios.

Yes you can use an app_config file to limit the number of apps per project although its nothing to do with cc_config and the ncpus element the OP was talking about.

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BOINC blog