trace/osnoise: Support hotplug operations

Enable and disable osnoise/timerlat thread during on CPU hotplug online
and offline operations respectivelly.

Link: https://lore.kernel.org/linux-doc/20210621134636.5b332226@oasis.local.home/
Link: https://lkml.kernel.org/r/39f98590b3caeb3c32f09526214058efe0e9272a.1624372313.git.bristot@redhat.com
Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 8546e66..38aa5e2 100644 (file)
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1416,22 +1416,67 @@ static int timerlat_main(void *data)
 #endif /* CONFIG_TIMERLAT_TRACER */
 
 /*
- * stop_per_cpu_kthread - stop per-cpu threads
+ * stop_kthread - stop a workload thread
+ */
+static void stop_kthread(unsigned int cpu)
+{
+       struct task_struct *kthread;
+
+       kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
+       if (kthread)
+               kthread_stop(kthread);
+       per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+}
+
+/*
+ * stop_per_cpu_kthread - Stop per-cpu threads
  *
  * Stop the osnoise sampling htread. Use this on unload and at system
  * shutdown.
  */
 static void stop_per_cpu_kthreads(void)
 {
-       struct task_struct *kthread;
        int cpu;
 
-       for_each_online_cpu(cpu) {
-               kthread = per_cpu(per_cpu_osnoise_var, cpu).kthread;
-               if (kthread)
-                       kthread_stop(kthread);
-               per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
+       get_online_cpus();
+
+       for_each_online_cpu(cpu)
+               stop_kthread(cpu);
+
+       put_online_cpus();
+}
+
+/*
+ * start_kthread - Start a workload tread
+ */
+static int start_kthread(unsigned int cpu)
+{
+       struct task_struct *kthread;
+       void *main = osnoise_main;
+       char comm[24];
+
+#ifdef CONFIG_TIMERLAT_TRACER
+       if (osnoise_data.timerlat_tracer) {
+               snprintf(comm, 24, "timerlat/%d", cpu);
+               main = timerlat_main;
+       } else {
+               snprintf(comm, 24, "osnoise/%d", cpu);
        }
+#else
+       snprintf(comm, 24, "osnoise/%d", cpu);
+#endif
+       kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
+
+       if (IS_ERR(kthread)) {
+               pr_err(BANNER "could not start sampling thread\n");
+               stop_per_cpu_kthreads();
+               return -ENOMEM;
+       }
+
+       per_cpu(per_cpu_osnoise_var, cpu).kthread = kthread;
+       wake_up_process(kthread);
+
+       return 0;
 }
 
 /*
@@ -1443,9 +1488,7 @@ static void stop_per_cpu_kthreads(void)
 static int start_per_cpu_kthreads(struct trace_array *tr)
 {
        struct cpumask *current_mask = &save_cpumask;
-       struct task_struct *kthread;
-       char comm[24];
-       void *main = osnoise_main;
+       int retval;
        int cpu;
 
        get_online_cpus();
@@ -1457,37 +1500,91 @@ static int start_per_cpu_kthreads(struct trace_array *tr)
         * And the CPU is online.
         */
        cpumask_and(current_mask, cpu_online_mask, current_mask);
-       put_online_cpus();
 
-       for_each_online_cpu(cpu)
+       for_each_possible_cpu(cpu)
                per_cpu(per_cpu_osnoise_var, cpu).kthread = NULL;
 
        for_each_cpu(cpu, current_mask) {
-#ifdef CONFIG_TIMERLAT_TRACER
-               if (osnoise_data.timerlat_tracer) {
-                       snprintf(comm, 24, "timerlat/%d", cpu);
-                       main = timerlat_main;
-               } else {
-                       snprintf(comm, 24, "osnoise/%d", cpu);
-               }
-#else
-               snprintf(comm, 24, "osnoise/%d", cpu);
-#endif
-               kthread = kthread_create_on_cpu(main, NULL, cpu, comm);
-
-               if (IS_ERR(kthread)) {
-                       pr_err(BANNER "could not start sampling thread\n");
+               retval = start_kthread(cpu);
+               if (retval) {
                        stop_per_cpu_kthreads();
-                       return -ENOMEM;
+                       return retval;
                }
-
-               per_cpu(per_cpu_osnoise_var, cpu).kthread = kthread;
-               wake_up_process(kthread);
        }
 
+       put_online_cpus();
+
        return 0;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+static void osnoise_hotplug_workfn(struct work_struct *dummy)
+{
+       struct trace_array *tr = osnoise_trace;
+       unsigned int cpu = smp_processor_id();
+
+
+       mutex_lock(&trace_types_lock);
+
+       if (!osnoise_busy)
+               goto out_unlock_trace;
+
+       mutex_lock(&interface_lock);
+       get_online_cpus();
+
+       if (!cpumask_test_cpu(cpu, &osnoise_cpumask))
+               goto out_unlock;
+
+       if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
+               goto out_unlock;
+
+       start_kthread(cpu);
+
+out_unlock:
+       put_online_cpus();
+       mutex_unlock(&interface_lock);
+out_unlock_trace:
+       mutex_unlock(&trace_types_lock);
+}
+
+static DECLARE_WORK(osnoise_hotplug_work, osnoise_hotplug_workfn);
+
+/*
+ * osnoise_cpu_init - CPU hotplug online callback function
+ */
+static int osnoise_cpu_init(unsigned int cpu)
+{
+       schedule_work_on(cpu, &osnoise_hotplug_work);
+       return 0;
+}
+
+/*
+ * osnoise_cpu_die - CPU hotplug offline callback function
+ */
+static int osnoise_cpu_die(unsigned int cpu)
+{
+       stop_kthread(cpu);
+       return 0;
+}
+
+static void osnoise_init_hotplug_support(void)
+{
+       int ret;
+
+       ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "trace/osnoise:online",
+                               osnoise_cpu_init, osnoise_cpu_die);
+       if (ret < 0)
+               pr_warn(BANNER "Error to init cpu hotplug support\n");
+
+       return;
+}
+#else /* CONFIG_HOTPLUG_CPU */
+static void osnoise_init_hotplug_support(void)
+{
+       return 0;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * osnoise_cpus_read - Read function for reading the "cpus" file
  * @filp: The active open file structure
@@ -1583,7 +1680,14 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
                osnoise_tracer_stop(tr);
 
        mutex_lock(&interface_lock);
+       /*
+        * osnoise_cpumask is read by CPU hotplug operations.
+        */
+       get_online_cpus();
+
        cpumask_copy(&osnoise_cpumask, osnoise_cpumask_new);
+
+       put_online_cpus();
        mutex_unlock(&interface_lock);
 
        if (running)
@@ -1940,6 +2044,7 @@ __init static int init_osnoise_tracer(void)
                return ret;
        }
 #endif
+       osnoise_init_hotplug_support();
 
        init_tracefs();