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CMake: Ninja pool jobs: tweak memory values.

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With adding more c++ and templates all over our code-base, the general
memory footprint of regulare and 'heavy' compile jobs have increased
over the past couple of years, reflect that in the heuristics used to
auto-compute default 'good enough' max number of compile and
heavy-complie jobs.
This commit is contained in:
Bastien Montagne
2025-07-08 13:05:51 +02:00
parent 065313eabe
commit 8322d0c463
1 changed files with 6 additions and 5 deletions
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11
CMakeLists.txt
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@@ -1790,10 +1790,11 @@ if("${CMAKE_GENERATOR}" MATCHES "Ninja" AND WITH_NINJA_POOL_JOBS)
# Note: this gives mem in MB.
cmake_host_system_information(RESULT _TOT_MEM QUERY TOTAL_PHYSICAL_MEMORY)
# Heuristics: Assume 8Gb of RAM is needed per heavy compile job.
# Typical RAM peak usage of these is actually less than 3GB currently,
# Heuristics: Assume 12Gb of RAM is needed per heavy compile job.
# Typical RAM peak usage of these is actually around 3-4GB currently,
# but this also accounts for the part of the physical RAM being used by other unrelated
# processes on the system, and the part being used by the 'regular' compile and linking jobs.
# Further more, some cycles kernel files can require almost 12GB in debug builds.
#
# Also always cap heavy jobs amount to `number of available threads - 1`,
# to ensure that even if there would be enough RAM, the machine never ends up
@@ -1809,7 +1810,7 @@ if("${CMAKE_GENERATOR}" MATCHES "Ninja" AND WITH_NINJA_POOL_JOBS)
# - debug with ASAN build:
# * RAM: typically less than 40%, with some peaks at 50%.
# * CPU: over 90% of usage on average over the whole build time.
math(EXPR _compile_heavy_jobs "${_TOT_MEM} / 8000")
math(EXPR _compile_heavy_jobs "${_TOT_MEM} / 12000")
math(EXPR _compile_heavy_jobs_max "${_NUM_CORES} - 1")
if(${_compile_heavy_jobs} GREATER ${_compile_heavy_jobs_max})
set(_compile_heavy_jobs ${_compile_heavy_jobs_max})
@@ -1826,7 +1827,7 @@ Define the maximum number of concurrent heavy compilation jobs, for ninja build
set(_compile_heavy_jobs)
set(_compile_heavy_jobs_max)
# Heuristics: Assume 2Gb of RAM is needed per heavy compile job.
# Heuristics: Assume 3Gb of RAM is needed per regular compile job.
# Typical RAM peak usage of these is actually way less than 1GB usually,
# but this also accounts for the part of the physical RAM being used by other unrelated
# processes on the system, and the part being used by the 'heavy' compile and linking jobs.
@@ -1835,7 +1836,7 @@ Define the maximum number of concurrent heavy compilation jobs, for ninja build
# `number of cores - 1`, otherwise allow using all cores if there is enough RAM available.
# This allows to ensure that the heavy jobs won't get starved by too many normal jobs,
# since the former usually take a long time to process.
math(EXPR _compile_jobs "${_TOT_MEM} / 2000")
math(EXPR _compile_jobs "${_TOT_MEM} / 3000")
if(${_NUM_CORES} GREATER 3)
math(EXPR _compile_jobs_max "${_NUM_CORES} - 1")
else()