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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
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@ -532,10 +532,12 @@ void __tasklet_hi_schedule(struct tasklet_struct *t)
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}
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EXPORT_SYMBOL(__tasklet_hi_schedule);
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static bool tasklet_should_run(struct tasklet_struct *t)
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static bool tasklet_clear_sched(struct tasklet_struct *t)
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{
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if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
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if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
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wake_up_var(&t->state);
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return true;
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}
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WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
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t->use_callback ? "callback" : "func",
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@ -563,7 +565,7 @@ static void tasklet_action_common(struct softirq_action *a,
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if (tasklet_trylock(t)) {
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if (!atomic_read(&t->count)) {
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if (tasklet_should_run(t)) {
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if (tasklet_clear_sched(t)) {
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if (t->use_callback)
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t->callback(t);
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else
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@ -623,13 +625,11 @@ void tasklet_kill(struct tasklet_struct *t)
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if (in_interrupt())
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pr_notice("Attempt to kill tasklet from interrupt\n");
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while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
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do {
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yield();
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} while (test_bit(TASKLET_STATE_SCHED, &t->state));
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}
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while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
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wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
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tasklet_unlock_wait(t);
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clear_bit(TASKLET_STATE_SCHED, &t->state);
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tasklet_clear_sched(t);
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}
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EXPORT_SYMBOL(tasklet_kill);
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