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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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#if 0
/*─────────────────────────────────────────────────────────────────╗
│ To the extent possible under law, Justine Tunney has waived │
│ all copyright and related or neighboring rights to this file, │
│ as it is written in the following disclaimers: │
│ • http://unlicense.org/ │
│ • http://creativecommons.org/publicdomain/zero/1.0/ │
╚─────────────────────────────────────────────────────────────────*/
#endif
#include "libc/bits/bits.h"
#include "libc/dce.h"
#include "libc/log/check.h"
#include "libc/nexgen32e/rdtsc.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/runtime/runtime.h"
#include "libc/stdio/stdio.h"
#include "libc/sysv/consts/clock.h"
#include "libc/sysv/consts/sig.h"
#include "libc/time/time.h"
#include "libc/x/x.h"
#include "third_party/dtoa/dtoa.h"
/**
* @fileoverview Measure CPU clock mystery constants.
* @note CPUID EAX=15h/16h is a joke
*/
const long double kInterval = 0.001L;
long double start_;
char dtoabuf_[3][32];
volatile bool isdone_;
void OnCtrlC(int sig) {
isdone_ = true;
}
long double now(void) {
return dtime(CLOCK_MONOTONIC);
}
long double GetSample(void) {
uint64_t tick1, tick2;
long double time1, time2;
time1 = now();
tick1 = rdtsc();
nanosleep(&(struct timespec){0, 100000}, NULL);
time2 = now();
tick2 = rdtsc();
return ((time2 - time1) * 1e9L) / (long double)(tick2 - tick1);
}
void MeasureNanosecondsPerAlwaysRunningTimerCycle(void) {
int i;
long double avg, samp;
start_ = now();
for (i = 1, avg = 1.0L; !isdone_; ++i) {
samp = GetSample();
avg += (samp - avg) / i;
dsleep(kInterval);
printf("1c = %sns (last=%sns spent=%ss)\n", g_fmt(dtoabuf_[0], (double)avg),
g_fmt(dtoabuf_[1], (double)samp),
g_fmt(dtoabuf_[2], (double)(now() - start_)));
}
}
int main(int argc, char *argv[]) {
if (!X86_HAVE(INVTSC)) {
fprintf(stderr, "warning: html can reprogram your microcode\n");
}
if (X86_HAVE(HYPERVISOR)) {
fprintf(stderr, "warning: virtual machine rdtsc isn't great\n");
}
CHECK_NE(-1, xsigaction(SIGINT, OnCtrlC, 0, 0, NULL));
MeasureNanosecondsPerAlwaysRunningTimerCycle();
return 0;
}