cache_achoustics.cpp

// ./a.out | aplay -r 256000 ?

#include <stdio.h>
#include <stdint.h>
#include <x86intrin.h>
#include <atomic>
#include <unistd.h>
#include <math.h>

std::atomic<uint8_t> caches[128 * 512 * 64];
int main(int argc) {

long double avg = 0;
auto tries = 1000UL;
long double slack = 0.01;
for(;;) {
long double min = 100000;
long double max = 0;

unsigned line = 0;

auto old_tries = tries;
auto new_tries = 0;
tries = 0;

for (;;)
{
line = line * 1 + line * 9 + line * 23 + (line / 7) * 314 ^ 0xDEFACE;
auto index = line % (sizeof(caches)/64);

_mm_mfence();
auto earlier = __rdtsc();
caches[index * 64 + 11]+= earlier;
_mm_mfence();
auto later = __rdtsc();

auto diff = later - earlier;
avg = avg + avg / (diff / 11.0) + diff;
avg = avg / (1 + 1.0/11 + 1);

max = max < avg? (max * 0.9 + avg * 0.1) : max*0.9999;
min = min > avg? (min * 0.9 + avg * 0.1) : min*1.0001;

auto i = abs(avg / max - 1);
auto q = abs(avg / min - 1);

tries++;
new_tries++;
if (new_tries > old_tries) {
new_tries -= old_tries;
slack *= 1.1;
//printf("RT: %p, %.8Lf i %.8Lf q %.8Lf\n", (void*)tries, slack, i, q);
}
slack = slack > 1? 0.99 : slack;
auto test = slack * slack * slack * slack;
if (i < test && q < test) {
if (new_tries == tries) {
slack = slack / 1.1;
}
if (argc==1)
printf("TM: %p avg: %.4Lf i:%.6Lf q:%.6Lf tries:%p slack: %.2Lf\n", (void*)later, avg, i, q, (void*)tries, slack);
else {
for (unsigned r = 0; r < (300 / avg); r++)
for (unsigned s = 0; s < avg; s++) {
auto phase = s / avg * 2 * 3.1415;
auto val = ((1+ sin(phase)) / 2 * q + i) / 2;
unsigned u = 128 * val;
u = u > 255? 255: u;
write(1, &u, 1);
}
}
usleep(1250);
break;
}
}
}