How to programmatically get the CPU cache page size in C++?

Question

I'd like my program to read the cache line size of the CPU it's running on in C++.

I know that this can't be done portably, so I will need a solution for Linux and another for Windows (Solutions for other systems could be usefull to others, so post them if you know them).

For Linux I could read the content of /proc/cpuinfo and parse the line begining with cache_alignment. Maybe there is a better way involving a call to an API.

For Windows I simply have no idea.

Answer 1

On Win32, GetLogicalProcessorInformation will give you back a SYSTEM_LOGICAL_PROCESSOR_INFORMATION which contains a CACHE_DESCRIPTOR, which has the information you need.

Answer 2

On Linux try the proccpuinfo library, an architecture independent C API for reading /proc/cpuinfo

Answer 3

For x86, the CPUID instruction. A quick google search reveals some libraries for win32 and c++. I have used CPUID via inline assembler as well.

Some more info:

• http://www.intel.com/Assets/PDF/appnote/241618.pdf
• http://softpixel.com/~cwright/programming/simd/cpuid.php

Answer 4

Looks like at least SCO unix (http://uw714doc.sco.com/en/man/html.3C/sysconf.3C.html) has _SC_CACHE_LINE for sysconf. Perhaps other platforms have something similar?

Answer 5

On Windows

#include <Windows.h>
#include <iostream>

using std::cout; using std::endl;

int main()
{
    SYSTEM_INFO systemInfo;
    GetSystemInfo(&systemInfo);
    cout << "Page Size Is: " << systemInfo.dwPageSize;
    getchar();
}

On Linux

http://linux.die.net/man/2/getpagesize

Answer 6

Here is sample code for those who wonder how to to utilize the function in accepted answer:

#include <new>
#include <iostream>
#include <Windows.h>


void ShowCacheSize()
{
    using CPUInfo = SYSTEM_LOGICAL_PROCESSOR_INFORMATION;
    DWORD len = 0;
    CPUInfo* buffer = nullptr;

    // Determine required length of a buffer
    if ((GetLogicalProcessorInformation(buffer, &len) == FALSE) && (GetLastError() == ERROR_INSUFFICIENT_BUFFER))
    {
        // Allocate buffer of required size
        buffer = new (std::nothrow) CPUInfo[len]{ };

        if (buffer == nullptr)
        {
            std::cout << "Buffer allocation of " << len << " bytes failed" << std::endl;
        }
        else if (GetLogicalProcessorInformation(buffer, &len) != FALSE)
        {
            for (DWORD i = 0; i < len; ++i)
            {
                // This will be true for multiple returned caches, we need just one
                if (buffer[i].Relationship == RelationCache)
                {
                    std::cout << "Cache line size is: " << buffer[i].Cache.LineSize << " bytes" << std::endl;
                    break;
                }
            }
        }
        else
        {
            std::cout << "ERROR: " << GetLastError() << std::endl;
        }

        delete[] buffer;
    }
}

Answer 7

I think you need NtQuerySystemInformation from ntdll.dll.