1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (C) 2023 Red Hat Inc, Daniel Bristot de Oliveira <bristot@kernel.org>
4  */
5 
6 #define _GNU_SOURCE
7 #include <sched.h>
8 #include <fcntl.h>
9 #include <stdlib.h>
10 #include <unistd.h>
11 #include <stdio.h>
12 #include <errno.h>
13 #include <string.h>
14 #include <tracefs.h>
15 #include <pthread.h>
16 #include <sys/wait.h>
17 #include <sys/prctl.h>
18 
19 #include "utils.h"
20 #include "timerlat_u.h"
21 
22 /*
23  * This is the user-space main for the tool timerlatu/ threads.
24  *
25  * It is as simple as this:
26  *  - set affinity
27  *  - set priority
28  *  - open tracer fd
29  *  - spin
30  *  - close
31  */
32 static int timerlat_u_main(int cpu, struct timerlat_u_params *params)
33 {
34 	struct sched_param sp = { .sched_priority = 95 };
35 	char buffer[1024];
36 	int timerlat_fd;
37 	cpu_set_t set;
38 	int retval;
39 
40 	/*
41 	 * This all is only setting up the tool.
42 	 */
43 	CPU_ZERO(&set);
44 	CPU_SET(cpu, &set);
45 
46 	retval = sched_setaffinity(gettid(), sizeof(set), &set);
47 	if (retval == -1) {
48 		debug_msg("Error setting user thread affinity %d, is the CPU online?\n", cpu);
49 		exit(1);
50 	}
51 
52 	if (!params->sched_param) {
53 		retval = sched_setscheduler(0, SCHED_FIFO, &sp);
54 		if (retval < 0) {
55 			err_msg("Error setting timerlat u default priority: %s\n", strerror(errno));
56 			exit(1);
57 		}
58 	} else {
59 		retval = __set_sched_attr(getpid(), params->sched_param);
60 		if (retval) {
61 			/* __set_sched_attr prints an error message, so */
62 			exit(0);
63 		}
64 	}
65 
66 	if (params->cgroup_name) {
67 		retval = set_pid_cgroup(gettid(), params->cgroup_name);
68 		if (!retval) {
69 			err_msg("Error setting timerlat u cgroup pid\n");
70 			pthread_exit(&retval);
71 		}
72 	}
73 
74 	/*
75 	 * This is the tool's loop. If you want to use as base for your own tool...
76 	 * go ahead.
77 	 */
78 	snprintf(buffer, sizeof(buffer), "osnoise/per_cpu/cpu%d/timerlat_fd", cpu);
79 
80 	timerlat_fd = tracefs_instance_file_open(NULL, buffer, O_RDONLY);
81 	if (timerlat_fd < 0) {
82 		err_msg("Error opening %s:%s\n", buffer, strerror(errno));
83 		exit(1);
84 	}
85 
86 	debug_msg("User-space timerlat pid %d on cpu %d\n", gettid(), cpu);
87 
88 	/* add should continue with a signal handler */
89 	while (true) {
90 		retval = read(timerlat_fd, buffer, 1024);
91 		if (retval < 0)
92 			break;
93 	}
94 
95 	close(timerlat_fd);
96 
97 	debug_msg("Leaving timerlat pid %d on cpu %d\n", gettid(), cpu);
98 	exit(0);
99 }
100 
101 /*
102  * timerlat_u_send_kill - send a kill signal for all processes
103  *
104  * Return the number of processes that received the kill.
105  */
106 static int timerlat_u_send_kill(pid_t *procs, int nr_cpus)
107 {
108 	int killed = 0;
109 	int i, retval;
110 
111 	for (i = 0; i < nr_cpus; i++) {
112 		if (!procs[i])
113 			continue;
114 		retval = kill(procs[i], SIGKILL);
115 		if (!retval)
116 			killed++;
117 		else
118 			err_msg("Error killing child process %d\n", procs[i]);
119 	}
120 
121 	return killed;
122 }
123 
124 /**
125  * timerlat_u_dispatcher - dispatch one timerlatu/ process per monitored CPU
126  *
127  * This is a thread main that will fork one new process for each monitored
128  * CPU. It will wait for:
129  *
130  *  - rtla to tell to kill the child processes
131  *  - some child process to die, and the cleanup all the processes
132  *
133  * whichever comes first.
134  *
135  */
136 void *timerlat_u_dispatcher(void *data)
137 {
138 	int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
139 	struct timerlat_u_params *params = data;
140 	char proc_name[128];
141 	int procs_count = 0;
142 	int retval = 1;
143 	pid_t *procs;
144 	int wstatus;
145 	pid_t pid;
146 	int i;
147 
148 	debug_msg("Dispatching timerlat u procs\n");
149 
150 	procs = calloc(nr_cpus, sizeof(pid_t));
151 	if (!procs)
152 		pthread_exit(&retval);
153 
154 	for (i = 0; i < nr_cpus; i++) {
155 		if (params->set && !CPU_ISSET(i, params->set))
156 			continue;
157 
158 		pid = fork();
159 
160 		/* child */
161 		if (!pid) {
162 
163 			/*
164 			 * rename the process
165 			 */
166 			snprintf(proc_name, sizeof(proc_name), "timerlatu/%d", i);
167 			pthread_setname_np(pthread_self(), proc_name);
168 			prctl(PR_SET_NAME, (unsigned long)proc_name, 0, 0, 0);
169 
170 			timerlat_u_main(i, params);
171 			/* timerlat_u_main should exit()! Anyways... */
172 			pthread_exit(&retval);
173 		}
174 
175 		/* parent */
176 		if (pid == -1) {
177 			timerlat_u_send_kill(procs, nr_cpus);
178 			debug_msg("Failed to create child processes");
179 			pthread_exit(&retval);
180 		}
181 
182 		procs_count++;
183 		procs[i] = pid;
184 	}
185 
186 	while (params->should_run) {
187 		/* check if processes died */
188 		pid = waitpid(-1, &wstatus, WNOHANG);
189 		if (pid != 0) {
190 			for (i = 0; i < nr_cpus; i++) {
191 				if (procs[i] == pid) {
192 					procs[i] = 0;
193 					procs_count--;
194 				}
195 			}
196 
197 			if (!procs_count)
198 				break;
199 		}
200 
201 		sleep(1);
202 	}
203 
204 	timerlat_u_send_kill(procs, nr_cpus);
205 
206 	while (procs_count) {
207 		pid = waitpid(-1, &wstatus, 0);
208 		if (pid == -1) {
209 			err_msg("Failed to monitor child processes");
210 			pthread_exit(&retval);
211 		}
212 		for (i = 0; i < nr_cpus; i++) {
213 			if (procs[i] == pid) {
214 				procs[i] = 0;
215 				procs_count--;
216 			}
217 		}
218 	}
219 
220 	params->stopped_running = 1;
221 
222 	free(procs);
223 	retval = 0;
224 	pthread_exit(&retval);
225 
226 }
227