https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105251
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> --- mongodb is using these two values incorrectly and even misunderstanding what they mean. hardware_constructive_interference_size means the Minimum offset between two objects which will avoid false sharing. So if you have two objects that are that distant apart, then there will be NO false sharing at all (some offsets smaller might also work too but it depends on the HW which is run on). While hardware_constructive_interference_size says the maxium offset between two obejcts which will promote true sharing. That is if the two objects are within that alignment, there is a guarantee that there will be sharing. So if they want to guarantee true sharing, then they need to have it as aligned to hardware_constructive_interference_size and make sure the size is smaller than hardware_constructive_interference_size . So In this case Together should be aligned to hardware_constructive_interference_size . The other CacheAligned cases need to be looked into make sure they are using the correct values too. Depending on what they are trying to do.
