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42 lines
1.5 KiB
C++
42 lines
1.5 KiB
C++
#include "getNumberOfPhysicalCPUCores.h"
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#if USE_CPUID
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# include <libcpuid/libcpuid.h>
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#endif
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#include <thread>
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unsigned getNumberOfPhysicalCPUCores()
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{
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static const unsigned number = []
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{
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# if USE_CPUID
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cpu_raw_data_t raw_data;
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cpu_id_t data;
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/// On Xen VMs, libcpuid returns wrong info (zero number of cores). Fallback to alternative method.
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/// Also, libcpuid does not support some CPUs like AMD Hygon C86 7151.
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if (0 != cpuid_get_raw_data(&raw_data) || 0 != cpu_identify(&raw_data, &data) || data.num_logical_cpus == 0)
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return std::thread::hardware_concurrency();
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unsigned res = data.num_cores * data.total_logical_cpus / data.num_logical_cpus;
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/// Also, libcpuid gives strange result on Google Compute Engine VMs.
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/// Example:
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/// num_cores = 12, /// number of physical cores on current CPU socket
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/// total_logical_cpus = 1, /// total number of logical cores on all sockets
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/// num_logical_cpus = 24. /// number of logical cores on current CPU socket
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/// It means two-way hyper-threading (24 / 12), but contradictory, 'total_logical_cpus' == 1.
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if (res != 0)
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return res;
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# endif
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/// As a fallback (also for non-x86 architectures) assume there are no hyper-threading on the system.
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/// (Actually, only Aarch64 is supported).
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return std::thread::hardware_concurrency();
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}();
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return number;
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}
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