timerlat_u.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2023 Red Hat Inc, Daniel Bristot de Oliveira <[email protected]>
 */

#define _GNU_SOURCE
#include <sched.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <tracefs.h>
#include <pthread.h>
#include <sys/wait.h>
#include <sys/prctl.h>

#include "utils.h"
#include "timerlat_u.h"

/*
 * This is the user-space main for the tool timerlatu/ threads.
 *
 * It is as simple as this:
 *  - set affinity
 *  - set priority
 *  - open tracer fd
 *  - spin
 *  - close
 */
static int timerlat_u_main(int cpu, struct timerlat_u_params *params)
{
	struct sched_param sp = { .sched_priority = 95 };
	char buffer[1024];
	int timerlat_fd;
	cpu_set_t set;
	int retval;

	/*
	 * This all is only setting up the tool.
	 */
	CPU_ZERO(&set);
	CPU_SET(cpu, &set);

	retval = sched_setaffinity(gettid(), sizeof(set), &set);
	if (retval == -1) {
		debug_msg("Error setting user thread affinity %d, is the CPU online?\n", cpu);
		exit(1);
	}

	if (!params->sched_param) {
		retval = sched_setscheduler(0, SCHED_FIFO, &sp);
		if (retval < 0)
			fatal("Error setting timerlat u default priority: %s", strerror(errno));
	} else {
		retval = __set_sched_attr(getpid(), params->sched_param);
		if (retval) {
			/* __set_sched_attr prints an error message, so */
			exit(0);
		}
	}

	if (params->cgroup_name) {
		retval = set_pid_cgroup(gettid(), params->cgroup_name);
		if (!retval) {
			err_msg("Error setting timerlat u cgroup pid\n");
			pthread_exit(&retval);
		}
	}

	/*
	 * This is the tool's loop. If you want to use as base for your own tool...
	 * go ahead.
	 */
	snprintf(buffer, sizeof(buffer), "osnoise/per_cpu/cpu%d/timerlat_fd", cpu);

	timerlat_fd = tracefs_instance_file_open(NULL, buffer, O_RDONLY);
	if (timerlat_fd < 0)
		fatal("Error opening %s:%s", buffer, strerror(errno));

	debug_msg("User-space timerlat pid %d on cpu %d\n", gettid(), cpu);

	/* add should continue with a signal handler */
	while (true) {
		retval = read(timerlat_fd, buffer, 1024);
		if (retval < 0)
			break;
	}

	close(timerlat_fd);

	debug_msg("Leaving timerlat pid %d on cpu %d\n", gettid(), cpu);
	exit(0);
}

/*
 * timerlat_u_send_kill - send a kill signal for all processes
 *
 * Return the number of processes that received the kill.
 */
static int timerlat_u_send_kill(pid_t *procs, int nr_cpus)
{
	int killed = 0;
	int i, retval;

	for (i = 0; i < nr_cpus; i++) {
		if (!procs[i])
			continue;
		retval = kill(procs[i], SIGKILL);
		if (!retval)
			killed++;
		else
			err_msg("Error killing child process %d\n", procs[i]);
	}

	return killed;
}

/**
 * timerlat_u_dispatcher - dispatch one timerlatu/ process per monitored CPU
 *
 * This is a thread main that will fork one new process for each monitored
 * CPU. It will wait for:
 *
 *  - rtla to tell to kill the child processes
 *  - some child process to die, and the cleanup all the processes
 *
 * whichever comes first.
 *
 */
void *timerlat_u_dispatcher(void *data)
{
	int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
	struct timerlat_u_params *params = data;
	char proc_name[128];
	int procs_count = 0;
	int retval = 1;
	pid_t *procs;
	int wstatus;
	pid_t pid;
	int i;

	debug_msg("Dispatching timerlat u procs\n");

	procs = calloc(nr_cpus, sizeof(pid_t));
	if (!procs)
		pthread_exit(&retval);

	for (i = 0; i < nr_cpus; i++) {
		if (params->set && !CPU_ISSET(i, params->set))
			continue;

		pid = fork();

		/* child */
		if (!pid) {

			/*
			 * rename the process
			 */
			snprintf(proc_name, sizeof(proc_name), "timerlatu/%d", i);
			pthread_setname_np(pthread_self(), proc_name);
			prctl(PR_SET_NAME, (unsigned long)proc_name, 0, 0, 0);

			timerlat_u_main(i, params);
			/* timerlat_u_main should exit()! Anyways... */
			pthread_exit(&retval);
		}

		/* parent */
		if (pid == -1) {
			timerlat_u_send_kill(procs, nr_cpus);
			debug_msg("Failed to create child processes");
			pthread_exit(&retval);
		}

		procs_count++;
		procs[i] = pid;
	}

	while (params->should_run) {
		/* check if processes died */
		pid = waitpid(-1, &wstatus, WNOHANG);
		if (pid != 0) {
			for (i = 0; i < nr_cpus; i++) {
				if (procs[i] == pid) {
					procs[i] = 0;
					procs_count--;
				}
			}

			if (!procs_count)
				break;
		}

		sleep(1);
	}

	timerlat_u_send_kill(procs, nr_cpus);

	while (procs_count) {
		pid = waitpid(-1, &wstatus, 0);
		if (pid == -1) {
			err_msg("Failed to monitor child processes");
			pthread_exit(&retval);
		}
		for (i = 0; i < nr_cpus; i++) {
			if (procs[i] == pid) {
				procs[i] = 0;
				procs_count--;
			}
		}
	}

	params->stopped_running = 1;

	free(procs);
	retval = 0;
	pthread_exit(&retval);

}