Commit 697d8c63 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

tasklets: Replace spin wait in tasklet_kill() 



tasklet_kill() spin waits for TASKLET_STATE_SCHED to be cleared invoking
yield() from inside the loop. yield() is an ill defined mechanism and the
result might still be wasting CPU cycles in a tight loop which is
especially painful in a guest when the CPU running the tasklet is scheduled
out.

tasklet_kill() is used in teardown paths and not performance critical at
all. Replace the spin wait with wait_var_event().

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309084241.890532921@linutronix.de
parent da044747

kernel/softirq.c

+9 −9
Original line number Diff line number Diff line
@@ -532,10 +532,12 @@ void __tasklet_hi_schedule(struct tasklet_struct *t) 
}

EXPORT_SYMBOL(__tasklet_hi_schedule);



static bool tasklet_should_run(struct tasklet_struct *t)

static bool tasklet_clear_sched(struct tasklet_struct *t)

{

	if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))

	if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {

		wake_up_var(&t->state);

		return true;

	}



	WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",

		  t->use_callback ? "callback" : "func",
@@ -563,7 +565,7 @@ static void tasklet_action_common(struct softirq_action *a, 


		if (tasklet_trylock(t)) {

			if (!atomic_read(&t->count)) {

				if (tasklet_should_run(t)) {

				if (tasklet_clear_sched(t)) {

					if (t->use_callback)

						t->callback(t);

					else
@@ -623,13 +625,11 @@ void tasklet_kill(struct tasklet_struct *t) 
	if (in_interrupt())

		pr_notice("Attempt to kill tasklet from interrupt\n");



	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {

		do {

			yield();

		} while (test_bit(TASKLET_STATE_SCHED, &t->state));

	}

	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))

		wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));



	tasklet_unlock_wait(t);

	clear_bit(TASKLET_STATE_SCHED, &t->state);

	tasklet_clear_sched(t);

}

EXPORT_SYMBOL(tasklet_kill);