Monday, 17 December 2012

Cross-platform function to get your cache line size

I wrote this function for a cache line aligned memory allocator which is for eventual use in my thread pool. It returns the line size (in bytes) of the host machine’s CPU cache, or 0 on failure. You can download it here. The source is 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

No comments:

Post a Comment