// SPDX-License-Identifier: GPL-2.0-or-later/* * Test null syscall performance * * Copyright (C) 2009-2015 Anton Blanchard, IBM */ #define NR_LOOPS 10000000 #include <string.h>#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <time.h>#include <sys/types.h>#include <sys/time.h>#include <sys/syscall.h>#include <signal.h> static volatile int soak_done;unsigned long long clock_frequency;unsigned long long timebase_frequency;double timebase_multiplier; static inline unsigned long mftb(void){	unsigned long low; 	asm volatile("mftb %0" : "=r" (low)); 	return low;} static void sigalrm_handler(int unused){	soak_done = 1;} /* * Use a timer instead of busy looping on clock_gettime() so we don't * pollute profiles with glibc and VDSO hits. */static void cpu_soak_usecs(unsigned long usecs){	struct itimerval val; 	memset(&val, 0, sizeof(val));	val.it_value.tv_usec = usecs; 	signal(SIGALRM, sigalrm_handler);	setitimer(ITIMER_REAL, &val, NULL); 	while (1) {		if (soak_done)			break;	} 	signal(SIGALRM, SIG_DFL);} /* * This only works with recent kernels where cpufreq modifies * /proc/cpuinfo dynamically. */static void get_proc_frequency(void){	FILE *f;	char line[128];	char *p, *end;	unsigned long v;	double d;	char *override; 	/* Try to get out of low power/low frequency mode */	cpu_soak_usecs(0.25 * 1000000); 	f = fopen("/proc/cpuinfo", "r");	if (f == NULL)		return; 	timebase_frequency = 0; 	while (fgets(line, sizeof(line), f) != NULL) {		if (strncmp(line, "timebase", 8) == 0) {			p = strchr(line, ':');			if (p != NULL) {				v = strtoull(p + 1, &end, 0);				if (end != p + 1)					timebase_frequency = v;			}		} 		if (((strncmp(line, "clock", 5) == 0) ||		     (strncmp(line, "cpu MHz", 7) == 0))) {			p = strchr(line, ':');			if (p != NULL) {				d = strtod(p + 1, &end);				if (end != p + 1) {					/* Find fastest clock frequency */					if ((d * 1000000ULL) > clock_frequency)						clock_frequency = d * 1000000ULL;				}			}		}	} 	fclose(f); 	override = getenv("FREQUENCY");	if (override)		clock_frequency = strtoull(override, NULL, 10); 	if (timebase_frequency)		timebase_multiplier = (double)clock_frequency					/ timebase_frequency;	else		timebase_multiplier = 1;} static void do_null_syscall(unsigned long nr){	unsigned long i; 	for (i = 0; i < nr; i++)		syscall(__NR_gettid);} #define TIME(A, STR) \ int main(void){	unsigned long tb_start, tb_now;	struct timespec tv_start, tv_now;	unsigned long long elapsed_ns, elapsed_tb; 	get_proc_frequency(); 	clock_gettime(CLOCK_MONOTONIC, &tv_start);	tb_start = mftb(); 	do_null_syscall(NR_LOOPS); 	clock_gettime(CLOCK_MONOTONIC, &tv_now);	tb_now = mftb(); 	elapsed_ns = (tv_now.tv_sec - tv_start.tv_sec) * 1000000000ULL +			(tv_now.tv_nsec - tv_start.tv_nsec);	elapsed_tb = tb_now - tb_start; 	printf("%10.2f ns %10.2f cycles\n", (float)elapsed_ns / NR_LOOPS,			(float)elapsed_tb * timebase_multiplier / NR_LOOPS); 	return 0;}