rtla/timerlat_top: Add timerlat user-space support

Add the support for running timerlat threads in user-space. In this
mode, enabled with -u/--user-threads, timerlat dispatches user-space
processes that will loop in the timerlat_fd, measuring the overhead
for going to user-space and then returning to the kernel - in addition
to the existing measurements.

Here is one example of the tool's output with -u enabled:

  $ sudo timerlat top -u -d 600 -q
                                       Timer Latency
    0 00:10:01   |          IRQ Timer Latency (us)        |         Thread Timer Latency (us)      |    Ret user Timer Latency (us)
  CPU COUNT      |      cur       min       avg       max |      cur       min       avg       max |      cur       min       avg       max
    0 #600001    |        0         0         0         3 |        2         1         2         9 |        3         2         3        15
    1 #600001    |        0         0         0         2 |        2         1         2        13 |        2         2         3        18
    2 #600001    |        0         0         0        10 |        2         1         2        16 |        3         2         3        20
    3 #600001    |        0         0         0         7 |        2         1         2        10 |        3         2         3        11
    4 #600000    |        0         0         0        16 |        2         1         2        41 |        3         2         3        58
    5 #600000    |        0         0         0         3 |        2         1         2        10 |        3         2         3        13
    6 #600000    |        0         0         0         5 |        2         1         2         7 |        3         2         3        10
    7 #600000    |        0         0         0         1 |        2         1         2         7 |        3         2         3        10

The tuning setup like -p or -C work for the user-space threads as well.

Link: https://lkml.kernel.org/r/758ad2292a0a1d884138d08219e1a0f572d257a2.1686066600.git.bristot@kernel.org

Cc: William White <chwhite@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 224 insertions, 0 deletions

diff --git a/tools/tracing/rtla/src/timerlat_u.c b/tools/tracing/rtla/src/timerlat_u.c
new file mode 100644
index 000000000000..05e310696dd5
--- /dev/null
+++ b/tools/tracing/rtla/src/timerlat_u.c
@@ -0,0 +1,224 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 Red Hat Inc, Daniel Bristot de Oliveira <bristot@kernel.org>
+ */
+
+#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) {
+		err_msg("Error setting user thread affinity\n");
+		exit(1);
+	}
+
+	if (!params->sched_param) {
+		retval = sched_setscheduler(0, SCHED_FIFO, &sp);
+		if (retval < 0) {
+			err_msg("Error setting timerlat u default priority: %s\n", strerror(errno));
+			exit(1);
+		}
+	} 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) {
+		err_msg("Error opening %s:%s\n", buffer, strerror(errno));
+		exit(1);
+	}
+
+	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--;
+				}
+			}
+			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);
+
+}