Commit 4998e7fd authored by Daniel Bristot de Oliveira's avatar Daniel Bristot de Oliveira Committed by Steven Rostedt (Google)
Browse files

tracing/osnoise: Switch from PF_NO_SETAFFINITY to migrate_disable 

Currently, osnoise/timerlat threads run with PF_NO_SETAFFINITY set.
It works well, however, cgroups do not allow PF_NO_SETAFFINITY threads
to be accepted, and this creates a limitation to osnoise/timerlat.

To avoid this limitation, disable migration of the threads as soon
as they start to run, and then clean the PF_NO_SETAFFINITY flag (still)
used during thread creation.

If for some reason a thread migration is requested, e.g., via
sched_settafinity, the tracer thread will notice and exit.

Link: https://lkml.kernel.org/r/8ba8bc9c15b3ea40cf73cf67a9bc061a264609f0.1686063934.git.bristot@kernel.org



Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: William White <chwhite@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarDaniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 83f74441

kernel/trace/trace_osnoise.c

+68 −0
Original line number Diff line number Diff line
@@ -1545,6 +1545,39 @@ static void osnoise_sleep(void) 
	}

}



/*

 * osnoise_migration_pending - checks if the task needs to migrate

 *

 * osnoise/timerlat threads are per-cpu. If there is a pending request to

 * migrate the thread away from the current CPU, something bad has happened.

 * Play the good citizen and leave.

 *

 * Returns 0 if it is safe to continue, 1 otherwise.

 */

static inline int osnoise_migration_pending(void)

{

	if (!current->migration_pending)

		return 0;



	/*

	 * If migration is pending, there is a task waiting for the

	 * tracer to enable migration. The tracer does not allow migration,

	 * thus: taint and leave to unblock the blocked thread.

	 */

	osnoise_taint("migration requested to osnoise threads, leaving.");



	/*

	 * Unset this thread from the threads managed by the interface.

	 * The tracers are responsible for cleaning their env before

	 * exiting.

	 */

	mutex_lock(&interface_lock);

	this_cpu_osn_var()->kthread = NULL;

	mutex_unlock(&interface_lock);



	return 1;

}



/*

 * osnoise_main - The osnoise detection kernel thread

 *
@@ -1553,12 +1586,29 @@ static void osnoise_sleep(void) 
 */

static int osnoise_main(void *data)

{

	unsigned long flags;



	/*

	 * This thread was created pinned to the CPU using PF_NO_SETAFFINITY.

	 * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread.

	 *

	 * To work around this limitation, disable migration and remove the

	 * flag.

	 */

	migrate_disable();

	raw_spin_lock_irqsave(&current->pi_lock, flags);

	current->flags &= ~(PF_NO_SETAFFINITY);

	raw_spin_unlock_irqrestore(&current->pi_lock, flags);



	while (!kthread_should_stop()) {

		if (osnoise_migration_pending())

			break;



		run_osnoise();

		osnoise_sleep();

	}



	migrate_enable();

	return 0;

}
@@ -1706,6 +1756,7 @@ static int timerlat_main(void *data) 
	struct timerlat_variables *tlat = this_cpu_tmr_var();

	struct timerlat_sample s;

	struct sched_param sp;

	unsigned long flags;

	u64 now, diff;



	/*
@@ -1714,6 +1765,18 @@ static int timerlat_main(void *data) 
	sp.sched_priority = DEFAULT_TIMERLAT_PRIO;

	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);



	/*

	 * This thread was created pinned to the CPU using PF_NO_SETAFFINITY.

	 * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread.

	 *

	 * To work around this limitation, disable migration and remove the

	 * flag.

	 */

	migrate_disable();

	raw_spin_lock_irqsave(&current->pi_lock, flags);

	current->flags &= ~(PF_NO_SETAFFINITY);

	raw_spin_unlock_irqrestore(&current->pi_lock, flags);



	tlat->count = 0;

	tlat->tracing_thread = false;
@@ -1731,6 +1794,7 @@ static int timerlat_main(void *data) 
	osn_var->sampling = 1;



	while (!kthread_should_stop()) {



		now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer));

		diff = now - tlat->abs_period;
@@ -1749,10 +1813,14 @@ static int timerlat_main(void *data) 
			if (time_to_us(diff) >= osnoise_data.stop_tracing_total)

				osnoise_stop_tracing();



		if (osnoise_migration_pending())

			break;



		wait_next_period(tlat);

	}



	hrtimer_cancel(&tlat->timer);

	migrate_enable();

	return 0;

}

#else /* CONFIG_TIMERLAT_TRACER */