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