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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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210309084241.890532921@linutronix.de
This commit is contained in:
Peter Zijlstra 2021-03-09 09:42:09 +01:00 committed by Thomas Gleixner
parent da04474740
commit 697d8c63c4
1 changed files with 9 additions and 9 deletions
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18
kernel/softirq.c
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@ -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);