Date: Wed, 5 May 2021 18:05:06 +0100 From: Vincent Donnefort <vincent.donnefort@....com> To: Alexander Monakov <amonakov@...ras.ru> Cc: musl@...ts.openwall.com Subject: Re: [PATCH] sysconf: add _SC_NPROCESSORS_CONF support On Wed, May 05, 2021 at 05:04:53PM +0300, Alexander Monakov wrote: > > > 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 > linux/Documentation/cputopology.txt > > Alexander Could indeed use one of the CPU mask. "present" is probably better suited for this usage. "possible" seems to have a different behavior on different architectures e.g it is CONFIG_HOTPLUG dependent on x86. Will do a V2 based on the present mask. -- Vincent
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