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Message-ID: <20210702132937.GA239501@e120877-lin.cambridge.arm.com>
Date: Fri, 2 Jul 2021 14:29:37 +0100
From: Vincent Donnefort <vincent.donnefort@....com>
To: jyknight@...gle.com, musl@...ts.openwall.com
Subject: Re: Re: [PATCH v2] sysconf: add _SC_NPROCESSORS_CONF support
Hi James,
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.
--
Vincent
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