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/* Measure nanosleep timer latency
* by: john stultz (john.stultz@linaro.org)
* (C) Copyright Linaro 2013
* Licensed under the GPLv2
*
* To build:
* $ gcc nsleep-lat.c -o nsleep-lat -lrt
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <string.h>
#include <signal.h>
#include "clock-helpers.h"
#include "kselftest.h"
#define UNRESONABLE_LATENCY (40 * NSEC_PER_MSEC)
struct timespec timespec_add(struct timespec ts, unsigned long long ns)
{
ts.tv_nsec += ns;
while (ts.tv_nsec >= NSEC_PER_SEC) {
ts.tv_nsec -= NSEC_PER_SEC;
ts.tv_sec++;
}
return ts;
}
long long timespec_sub(struct timespec a, struct timespec b)
{
long long ret = NSEC_PER_SEC * b.tv_sec + b.tv_nsec;
ret -= NSEC_PER_SEC * a.tv_sec + a.tv_nsec;
return ret;
}
int nanosleep_lat_test(int clockid, long long ns)
{
struct timespec start, end, target;
long long latency = 0;
int i, count;
target.tv_sec = ns/NSEC_PER_SEC;
target.tv_nsec = ns%NSEC_PER_SEC;
if (clock_gettime(clockid, &start))
return KSFT_SKIP;
if (clock_nanosleep(clockid, 0, &target, NULL))
return KSFT_SKIP;
count = 10;
/* First check relative latency */
if (clock_gettime(clockid, &start))
return KSFT_FAIL;
for (i = 0; i < count; i++) {
if (clock_nanosleep(clockid, 0, &target, NULL))
return KSFT_FAIL;
}
if (clock_gettime(clockid, &end))
return KSFT_FAIL;
if (((timespec_sub(start, end)/count)-ns) > UNRESONABLE_LATENCY) {
ksft_print_msg("Large rel latency: %lld ns :", (timespec_sub(start, end)/count)-ns);
return KSFT_FAIL;
}
/* Next check absolute latency */
for (i = 0; i < count; i++) {
if (clock_gettime(clockid, &start))
return KSFT_FAIL;
target = timespec_add(start, ns);
if (clock_nanosleep(clockid, TIMER_ABSTIME, &target, NULL))
return KSFT_FAIL;
if (clock_gettime(clockid, &end))
return KSFT_FAIL;
latency += timespec_sub(target, end);
}
if (latency/count > UNRESONABLE_LATENCY) {
ksft_print_msg("Large abs latency: %lld ns :", latency/count);
return KSFT_FAIL;
}
return KSFT_PASS;
}
int main(int argc, char **argv)
{
long long length;
int clockid, ret;
static const clockid_t tested_clocks[] = {
CLOCK_REALTIME,
CLOCK_MONOTONIC,
CLOCK_BOOTTIME,
CLOCK_BOOTTIME_ALARM,
CLOCK_REALTIME_ALARM,
CLOCK_TAI,
};
ksft_print_header();
ksft_set_plan(ARRAY_SIZE(tested_clocks));
for (size_t clock_index = 0; clock_index < ARRAY_SIZE(tested_clocks); clock_index++) {
clockid = tested_clocks[clock_index];
length = 10;
while (length <= (NSEC_PER_SEC * 10)) {
ret = nanosleep_lat_test(clockid, length);
if (ret)
break;
length *= 100;
}
ksft_test_result_report(ret, "%s\n", clock_name(clockid));
}
ksft_finished();
}
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