Programmatically get the cache line size?

On Linux (with a reasonably recent kernel), you can get this information out of /sys:

/sys/devices/system/cpu/cpu0/cache/

This directory has a subdirectory for each level of cache. Each of those directories contains the following files:

coherency_line_sizelevelnumber_of_setsphysical_line_partitionshared_cpu_listshared_cpu_mapsizetypeways_of_associativity

This gives you more information about the cache then you'd ever hope to know, including the cacheline size (coherency_line_size) as well as what CPUs share this cache. This is very useful if you are doing multithreaded programming with shared data (you'll get better results if the threads sharing data are also sharing a cache).

On Linux look at sysconf(3).

sysconf (_SC_LEVEL1_DCACHE_LINESIZE)

You can also get it from the command line using getconf:

$ getconf LEVEL1_DCACHE_LINESIZE64

I have been working on some cache line stuff and needed to write a cross-platform function. I committed it to a github repo at https://github.com/NickStrupat/CacheLineSize, or you can just use the source below. Feel free to do whatever you want with it.

#ifndef GET_CACHE_LINE_SIZE_H_INCLUDED#define GET_CACHE_LINE_SIZE_H_INCLUDED// Author: Nick Strupat// Date: October 29, 2010// Returns the cache line size (in bytes) of the processor, or 0 on failure#include <stddef.h>size_t cache_line_size();#if defined(__APPLE__)#include <sys/sysctl.h>size_t cache_line_size() {    size_t line_size = 0;    size_t sizeof_line_size = sizeof(line_size);    sysctlbyname("hw.cachelinesize", &line_size, &sizeof_line_size, 0, 0);    return line_size;}#elif defined(_WIN32)#include <stdlib.h>#include <windows.h>size_t cache_line_size() {    size_t line_size = 0;    DWORD buffer_size = 0;    DWORD i = 0;    SYSTEM_LOGICAL_PROCESSOR_INFORMATION * buffer = 0;    GetLogicalProcessorInformation(0, &buffer_size);    buffer = (SYSTEM_LOGICAL_PROCESSOR_INFORMATION *)malloc(buffer_size);    GetLogicalProcessorInformation(&buffer[0], &buffer_size);    for (i = 0; i != buffer_size / sizeof(SYSTEM_LOGICAL_PROCESSOR_INFORMATION); ++i) {        if (buffer[i].Relationship == RelationCache && buffer[i].Cache.Level == 1) {            line_size = buffer[i].Cache.LineSize;            break;        }    }    free(buffer);    return line_size;}#elif defined(linux)#include <stdio.h>size_t cache_line_size() {    FILE * p = 0;    p = fopen("/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size", "r");    unsigned int i = 0;    if (p) {        fscanf(p, "%d", &i);        fclose(p);    }    return i;}#else#error Unrecognized platform#endif#endif