How to get number of physical CPU:s in Linux using C?

Question

I am aware that sysconf(_SC_NPROCESSORS_ONLN) will give me the number of logical processors. But how can I get the number of physical processors?

score 3 · Answer 1 · answered Feb 25 '11 at 14:22

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@Havoc P: offline cpus aren't shown in /proc/cpuinfo .

CPU topology is described by /sys/devices/system/cpu/cpu*/topology/*

answered Feb 25 '11 at 14:22

adobriyan

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score 1 · Answer 2 · answered Feb 25 '11 at 14:10

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You could parse /proc/cpuinfo and count the number of distinct "physical id:" lines. Sort of annoying, but I don't know if there's a better option. If you're using GLib or another library with regex support it'd be easier. Or you could popen() a command line to do it if you're feeling really hacky. example command line at: http://www.brandonhutchinson.com/Understanding_proc_cpuinfo.html

answered Feb 25 '11 at 14:10

Havoc P

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POSIX regex support (BRE and ERE) is part of the standard library on any POSIX system, including Linux. No need for glib. – R.. GitHub STOP HELPING ICE Feb 25 '11 at 19:44

score 1 · Answer 3 · answered Feb 25 '11 at 14:55

I think the best way to get this information is to use hwloc: http://www.open-mpi.org/projects/hwloc/.

They provide a bunch of user tools that let you get at the cpu topology of a system, but they also provide a library that you can use from C: http://www.open-mpi.org/projects/hwloc/doc/v1.1.1/#interface

score 0 · Answer 4 · edited May 23 '17 at 12:33

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Perhaps this answer to a similar question does help. There's a comment about the code not being correct, but it could be a good starting point.

edited May 23 '17 at 12:33

Community

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answered Feb 25 '11 at 14:06

schnaader

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How to get number of physical CPU:s in Linux using C?

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