ClickHouse/dbms/Common/getNumberOfPhysicalCPUCores.cpp

#include <Common/getNumberOfPhysicalCPUCores.h>
#include <thread>

#include <Common/config.h>
#if USE_CPUID
#   include <libcpuid/libcpuid.h>
#elif USE_CPUINFO
#   include <cpuinfo.h>
#endif


unsigned getNumberOfPhysicalCPUCores()
{
#if USE_CPUID
    cpu_raw_data_t raw_data;
    cpu_id_t data;

    /// On Xen VMs, libcpuid returns wrong info (zero number of cores). Fallback to alternative method.
    /// Also, libcpuid does not support some CPUs like AMD Hygon C86 7151.
    if (0 != cpuid_get_raw_data(&raw_data) || 0 != cpu_identify(&raw_data, &data) || data.num_logical_cpus == 0)
        return std::thread::hardware_concurrency();

    unsigned res = data.num_cores * data.total_logical_cpus / data.num_logical_cpus;

    /// Also, libcpuid gives strange result on Google Compute Engine VMs.
    /// Example:
    ///  num_cores = 12,            /// number of physical cores on current CPU socket
    ///  total_logical_cpus = 1,    /// total number of logical cores on all sockets
    ///  num_logical_cpus = 24.     /// number of logical cores on current CPU socket
    /// It means two-way hyper-threading (24 / 12), but contradictory, 'total_logical_cpus' == 1.

    if (res != 0)
        return res;

#elif USE_CPUINFO
    uint32_t cores = 0;
    if (cpuinfo_initialize())
        cores = cpuinfo_get_cores_count();

    if (cores)
        return cores;
#endif

    /// As a fallback (also for non-x86 architectures) assume there are no hyper-threading on the system.
    /// (Actually, only Aarch64 is supported).
    return std::thread::hardware_concurrency();
}