Date: Sat, 3 Jul 2021 23:20:18 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: Vincent Donnefort <vincent.donnefort@....com> Cc: jyknight@...gle.com, musl@...ts.openwall.com Subject: Re: Re: Re: [PATCH v2] sysconf: add _SC_NPROCESSORS_CONF support * Vincent Donnefort <vincent.donnefort@....com> [2021-07-02 14:29:37 +0100]: > Here's a new thread as I never received your previous email and I just > noticed the answer today. > > I'm not sure I understand why I can't use "present". As per the kernel > documentation: > > possible: CPUs that have been allocated resources and can be > brought online if they are present. [cpu_possible_mask] > > present: CPUs that have been identified as being present in the > system. [cpu_present_mask] > > > In this example, the NR_CPUS config option is 128, but the kernel was > started with possible_cpus=144. There are 4 CPUs in the system and cpu2 > was manually taken offline (and is the only CPU that can be brought > online.):: > > kernel_max: 127 > offline: 2,4-127,128-143 > online: 0-1,3 > possible: 0-127 > present: 0-3 > > So indeed I could use "possible"... but there's a chance the two masks won't > be equal, and the sysfs entries are matching "present", not "possible". > > "possible" is the CPUs that have allocated resources and can be physically > added to the system. "present" is the CPUs that are known as physically > present but might be offline. i guess we just need a guarantee that these interfaces are stable and the set of present cpus don't change during the lifetime of a process. (can that even work with checkpoint/restore? probably not our problem)
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