Tom,
trix@xxxxxxxxxx writes:
> From: Tom Rix <trix@xxxxxxxxxx>
>
> jitterz is a program for measuring system jitter.
The exact purpose of this is?
> +
> +#define CHECK_LOST_TIME() \
> + do { \
> + if (d >= dt_min) { \
> + lt += d; \
> + for (j = 16; j > 0; j--) { \
> + if (d >= b[j - 1].s) { \
> + b[j - 1].c = \
> + b[j - 1].c + 1; \
> + break; \
> + } \
> + } \
> + } \
> + } while (0) \
Aside of having a \ at the last line, macros which rely on variable
names at the call site are broken to begin with. What's so magic to hide
this in a macro instead of writing a proper function?
> +static inline uint64_t tsc(void)
> +{
> + uint64_t ret = 0;
> + uint32_t l, h;
> +
> + __asm__ __volatile__("lfence");
> + __asm__ __volatile__("rdtsc" : "=a"(l), "=d"(h));
> + ret = ((uint64_t)h << 32) | l;
> + return ret;
> +}
Having x86 specific code in a generic test suite is a non starter.
> +static int move_to_core(int core_i)
> +{
> + cpu_set_t cpus;
> +
> + CPU_ZERO(&cpus);
> + CPU_SET(core_i, &cpus);
> + return sched_setaffinity(0, sizeof(cpus), &cpus);
> +}
> +
> +static int set_sched(void)
> +{
> + struct sched_param p = { 0 };
> +
> + p.sched_priority = priority;
> + return sched_setscheduler(0, policy, &p);
> +}
> +
> +static long read_cpuinfo_cur_freq(int core_i)
> +{
> + uint64_t fs = -1;
> + char path[80];
> + struct stat sb;
> + int i;
> + char *freq[2] = {
> + "cpuinfo_cur_freq",
> + /* assumes a busy wait will be run at the max freq */
Assumptions in tools which are meant to provide useful output are really
not useful at all.
> + "cpuinfo_max_freq",
> + };
> + for (i = 0; i < 2; i++) {
> + snprintf(path, 80,
> + "/sys/devices/system/cpu/cpu%d/cpufreq/%s",
> + core_i, freq[1]);
> + if (!stat(path, &sb)) {
> + FILE *f = 0;
> +
> + f = fopen(path, "rt");
> + if (f) {
> + fscanf(f, "%lu", &fs);
That definitely has never seen a 32bit compile.
> + fclose(f);
> + } else {
> + perror(path);
> + }
> + } else {
> + perror(path);
> + }
> + }
> +
> + if (fs == (uint64_t) -1) {
So here you have a typecast but at the place where this is initialized
this is not required, right?
> + printf("Error reading CPU frequency for core %d\n", core_i);
> + exit(1);
> + }
> + return fs;
> +}
> +
> +int main(int argc, char **argv)
> +{
> + int max_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> + struct timespec tvs, tve;
> + double sec;
> + uint64_t fs, fe, fr;
> + unsigned int i, j, rt = 60;
> + uint64_t dt = 1500;
> + struct bucket {
> + uint64_t s;
> + uint64_t c;
> + } b[16];
> + uint64_t frs, fre, lt;
> +
> + process_options(argc, argv, max_cpus);
> +
> + /* return of this function must be tested for success */
> + if (move_to_core(cpu) != 0) {
> + printf("Error while setting thread affinity to cpu %d!", cpu);
> + exit(1);
> + }
> + if (set_sched() != 0) {
> + printf("Error while setting %s policy, priority %d!",
> + policyname(policy), priority);
> + exit(1);
> + }
> +
> + fr = fs = 0;
> + fe = 1;
> + while (fs != fe) {
> +retry:
> + if (!fr) {
> + fs = read_cpuinfo_cur_freq(cpu);
> + fe = 0;
> + } else {
> + fs = fr;
> + }
> + uint64_t dt_min = (dt * fs) / 1000000;
> +
> + lt = 0;
> + for (j = 0; j < 16; j++) {
> + b[j].c = 0;
> + if (j == 0)
> + b[j].s = dt_min;
> + else
> + b[j].s = b[j - 1].s * 2;
> + }
> + fs *= 1000;
> +
> + frs = tsc();
> + clock_gettime(CLOCK_MONOTONIC_RAW, &tvs);
> +
> + for (i = 0; i < rt; i++) {
> + uint64_t s, e, so;
> +
> + s = tsc();
> + e = s;
> + e += fs;
> + if (e < s)
> + goto retry;
> + so = s;
> +
> + while (1) {
> + uint64_t d;
> +
> + s = tsc();
> + if (s == so)
> + continue;
> +
> + d = s - so;
> + CHECK_LOST_TIME();
> + if (s >= e)
> + break;
> + so = s;
> + }
> + }
> + fre = tsc();
> + clock_gettime(CLOCK_MONOTONIC_RAW, &tve);
> + sec = tve.tv_sec - tvs.tv_sec +
> + (tve.tv_nsec - tvs.tv_nsec) / 1e9;
> + if ((fabs(sec - rt) / (double)rt) > 0.01) {
> + if (fre > frs) {
> + fr = (fre - frs) / (1000 * sec);
> + fe = fr * 1000;
> + }
> + goto retry;
> + }
> + if (!fr) {
> + fe = read_cpuinfo_cur_freq(cpu);
> + fe *= 1000;
> + }
> + }
> + for (j = 0; j < 16; j++)
> + printf("%lu\n", b[j].c);
> +
> + if (lt != fs) {
> + printf("Lost time %f\n", (double)lt / (double)fs);
> + return 1;
> + }
> +
> + return 0;
As the above is completely unreadable gibberish I can only assume that I
wasted time staring at a well done April 1st joke :)
Thanks,
tglx
