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/* Clear the CPU cache for benchmark purposes. Pretty simple minded.
* Might not work in some complex cache topologies.
* When you switch CPUs it's a good idea to clear the cache after testing
* too.
*/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include "clearcache.h"
static unsigned cache_size(void)
{
unsigned cs = 0;
#ifdef _SC_LEVEL1_DCACHE_SIZE
cs += sysconf(_SC_LEVEL1_DCACHE_SIZE);
#endif
#ifdef _SC_LEVEL2_CACHE_SIZE
cs += sysconf(_SC_LEVEL2_CACHE_SIZE);
#endif
#ifdef _SC_LEVEL3_CACHE_SIZE
cs += sysconf(_SC_LEVEL3_CACHE_SIZE);
#endif
#ifdef _SC_LEVEL4_CACHE_SIZE
cs += sysconf(_SC_LEVEL4_CACHE_SIZE);
#endif
if (cs == 0) {
static int warned;
if (!warned) {
printf("Cannot determine CPU cache size\n");
warned = 1;
}
cs = 64*1024*1024;
}
cs *= 2; /* safety factor */
return cs;
}
static void fallback_clearcache(void)
{
static unsigned char *clearmem;
unsigned cs = cache_size();
unsigned i;
if (!clearmem)
clearmem = malloc(cs);
if (!clearmem) {
printf("Warning: cannot allocate %u bytes of clear cache buffer\n", cs);
return;
}
for (i = 0; i < cs; i += 32)
clearmem[i] = 1;
}
void clearcache(unsigned char *mem, unsigned size)
{
#if defined(__i386__) || defined(__x86_64__)
unsigned i, cl, eax, feat;
/* get clflush unit and feature */
asm("cpuid" : "=a" (eax), "=b" (cl), "=d" (feat) : "0" (1) : "cx");
if (!(feat & (1 << 19)))
fallback_clearcache();
cl = ((cl >> 8) & 0xff) * 8;
for (i = 0; i < size; i += cl)
asm("clflush %0" :: "m" (mem[i]));
#elif defined(__ia64__)
unsigned long cl, endcl;
// flush probable 128 byte cache lines (but possibly 64 bytes)
cl = (unsigned long)mem;
endcl = (unsigned long)(mem + (size-1));
for (; cl <= endcl; cl += 64)
asm ("fc %0" :: "r"(cl) : "memory" );
#else
#warning "Consider adding a clearcache implementation for your architecture"
fallback_clearcache();
#endif
}
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