linux/samples/trace_events/trace-events-sample.c
Sebastian Andrzej Siewior 3bd3706251 sched/core: Provide a pointer to the valid CPU mask
In commit:

  4b53a3412d ("sched/core: Remove the tsk_nr_cpus_allowed() wrapper")

the tsk_nr_cpus_allowed() wrapper was removed. There was not
much difference in !RT but in RT we used this to implement
migrate_disable(). Within a migrate_disable() section the CPU mask is
restricted to single CPU while the "normal" CPU mask remains untouched.

As an alternative implementation Ingo suggested to use:

	struct task_struct {
		const cpumask_t		*cpus_ptr;
		cpumask_t		cpus_mask;
        };
with
	t->cpus_ptr = &t->cpus_mask;

In -RT we then can switch the cpus_ptr to:

	t->cpus_ptr = &cpumask_of(task_cpu(p));

in a migration disabled region. The rules are simple:

 - Code that 'uses' ->cpus_allowed would use the pointer.
 - Code that 'modifies' ->cpus_allowed would use the direct mask.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190423142636.14347-1-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-06-03 11:49:37 +02:00

141 lines
2.9 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/kthread.h>
/*
* Any file that uses trace points, must include the header.
* But only one file, must include the header by defining
* CREATE_TRACE_POINTS first. This will make the C code that
* creates the handles for the trace points.
*/
#define CREATE_TRACE_POINTS
#include "trace-events-sample.h"
static const char *random_strings[] = {
"Mother Goose",
"Snoopy",
"Gandalf",
"Frodo",
"One ring to rule them all"
};
static void simple_thread_func(int cnt)
{
int array[6];
int len = cnt % 5;
int i;
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(HZ);
for (i = 0; i < len; i++)
array[i] = i + 1;
array[i] = 0;
/* Silly tracepoints */
trace_foo_bar("hello", cnt, array, random_strings[len],
current->cpus_ptr);
trace_foo_with_template_simple("HELLO", cnt);
trace_foo_bar_with_cond("Some times print", cnt);
trace_foo_with_template_cond("prints other times", cnt);
trace_foo_with_template_print("I have to be different", cnt);
}
static int simple_thread(void *arg)
{
int cnt = 0;
while (!kthread_should_stop())
simple_thread_func(cnt++);
return 0;
}
static struct task_struct *simple_tsk;
static struct task_struct *simple_tsk_fn;
static void simple_thread_func_fn(int cnt)
{
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(HZ);
/* More silly tracepoints */
trace_foo_bar_with_fn("Look at me", cnt);
trace_foo_with_template_fn("Look at me too", cnt);
}
static int simple_thread_fn(void *arg)
{
int cnt = 0;
while (!kthread_should_stop())
simple_thread_func_fn(cnt++);
return 0;
}
static DEFINE_MUTEX(thread_mutex);
static int simple_thread_cnt;
int foo_bar_reg(void)
{
mutex_lock(&thread_mutex);
if (simple_thread_cnt++)
goto out;
pr_info("Starting thread for foo_bar_fn\n");
/*
* We shouldn't be able to start a trace when the module is
* unloading (there's other locks to prevent that). But
* for consistency sake, we still take the thread_mutex.
*/
simple_tsk_fn = kthread_run(simple_thread_fn, NULL, "event-sample-fn");
out:
mutex_unlock(&thread_mutex);
return 0;
}
void foo_bar_unreg(void)
{
mutex_lock(&thread_mutex);
if (--simple_thread_cnt)
goto out;
pr_info("Killing thread for foo_bar_fn\n");
if (simple_tsk_fn)
kthread_stop(simple_tsk_fn);
simple_tsk_fn = NULL;
out:
mutex_unlock(&thread_mutex);
}
static int __init trace_event_init(void)
{
simple_tsk = kthread_run(simple_thread, NULL, "event-sample");
if (IS_ERR(simple_tsk))
return -1;
return 0;
}
static void __exit trace_event_exit(void)
{
kthread_stop(simple_tsk);
mutex_lock(&thread_mutex);
if (simple_tsk_fn)
kthread_stop(simple_tsk_fn);
simple_tsk_fn = NULL;
mutex_unlock(&thread_mutex);
}
module_init(trace_event_init);
module_exit(trace_event_exit);
MODULE_AUTHOR("Steven Rostedt");
MODULE_DESCRIPTION("trace-events-sample");
MODULE_LICENSE("GPL");