CMSSW_14_0_X and above releases are build for multiple micro-architectures support for x86_64.
CMSSW_14_0, CMSSW_14_1 and CMSSW_14_2 use x86-64-v2 as default micro-architecture while x86-64-v3 is provided as an additional micro-architectures. In order to save time and resources, by default SCRAM is configured to used only x86-64-v2. But if you need to use x86-64-v3 set of librairies/plugins of cmssw then you can run scram build enable-multi-targets in your developer area. This will allow scram to build your checked out packages for both micro-archs and automatiically select the best set of libraries at runtime.
Starting with CMSSW_15_0_X, we have the follow changes
x86-64-v3x86-64-v2CMSSW release (e.g. running cmsenv directly from the release path) will automatically select the best micro-architecture e.g.
x86-64-v2 set of libraries/pluginsx86-64-v3 set of libraries/plugisnSCRAM will create developer area with multi-microarchitecture support enabled. Any checked out packages will be build for both micro-architectures. At runtime SCRAM will selected the best matching micro-architectureSCRAM will create developer area with multi-microarchitecture support disabled. Any checked out packages will only be built for default (x86-64-v3) micro-architecture. At runtime SCRAM will only use default (x86-64-v3) micro-architecture libraries.SCRAM will also set following environment variables for CMSSW_15_0 and above
CMSSW_15_0_X it will be x86-64-v3CMSSW_15_0, is developer area has multi-microarchitecture support enabled then SCRAM_MIN_SUPPORTED_MICROARCH will be set to x86-64-v2 otherwise it will be x86-64-v3