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Date: Wed, 5 May 2021 17:04:53 +0300 (MSK)
From: Alexander Monakov <>
cc: Vincent Donnefort <>
Subject: Re: [PATCH] sysconf: add _SC_NPROCESSORS_CONF support

On Wed, 5 May 2021, Vincent Donnefort wrote:

> Currently, _SC_NPROCESSORS_CONF is always equal to _SC_NPROCESSORS_ONLN.
> However, it is expected from the first one to give the total number of CPUs
> in the system, while the later must return only the number of CPUs which
> are currently online. This distinction is important for a software such as
> trace-cmd. Trace-cmd is a front-end for the kernel tracing tool ftrace.
> When recording traces, trace-cmd needs to get the total number of CPUs
> available in the system (_SC_NPROCESSORS_CONF) and not only the online ones
> otherwise if a CPU goes offline some data might be missing.
> Hence, add a specific method to get _SC_NPROCESSORS_CONF, based on the
> sysfs CPU entries /sys/devices/system/cpu/cpu[0-9]

Why do the opendir instead of reading from /sys/devices/system/cpu/possible?
The online/offline/possible CPU masks are documented in
linux/Documentation/ABI/testing/sysfs-devices-system-cpu and


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