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Set system test threads default based on CPU count #40785

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thomashampson wants to merge 2 commits into from
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Set system test threads default based on CPU count #40785

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d955ecb
Set default system test threads to 3/16 of n cores.
thomashampson Jan 30, 2026
31b4195
Ensure at least one thread for system tests
thomashampson Jan 30, 2026
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9 changes: 6 additions & 3 deletions buildconfig/Jenkins/Conda/run-tests
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Expand Up @@ -20,10 +20,13 @@ BUILD_THREADS=$6

XVFB_SERVER_NUM=101

# If this isn't specified for a Jenkins agent, revert to default value
# If this isn't specified for a machine, revert to default value
if [[ -z "$BUILD_THREADS_SYSTEM_TESTS" ]]; then
# Default to 3 system tests running in parallel, assuming builders have >= 32GB RAM
BUILD_THREADS_SYSTEM_TESTS=3
# Default to a 3/16 fraction of the build threads, e.g. 8 for a 32-core machine,
# to allow enough RAM for concurrently running system tests.
BUILD_THREADS_SYSTEM_TESTS=$(( BUILD_THREADS * 3 / 16 ))
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@cailafinn cailafinn Feb 9, 2026

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Do you think we need to make sure this is an integer here? I'm just considering the STFC Cloud might change again and not have a nicely divisible number of cores.

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@thomashampson thomashampson Feb 11, 2026

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This will do integer division, so will take the floor. However, thinking about it more, maybe we should use RAM to determine the system test threads. E.g. our Windows runners currently have 16GB RAM and 24 cores. With the above calculation, that would mean 4 system test threads, but we are currently limiting to 2. What do you think?

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@cailafinn cailafinn Feb 11, 2026

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I think that's probably more sensible, since RAM is the bottleneck for the problem we're solving by restricting anyway.

# Ensure at least 1 thread
(( BUILD_THREADS_SYSTEM_TESTS < 1 )) && BUILD_THREADS_SYSTEM_TESTS=1
fi

# Jenkins nodes may specify the maximum number of unit tests to run in parallel.
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