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Commit 74bdf781 authored by Eric Dumazet's avatar Eric Dumazet Committed by Thomas Gleixner
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genirq: Speedup show_interrupts() 



Since commit 425a5072 ("genirq: Free irq_desc with rcu"),
show_interrupts() can be switched to rcu locking, which removes possible
contention on sparse_irq_lock.

The per_cpu count scan and print can be done without holding desc spinlock.

And there is no need to call kstat_irqs_cpu() and abuse irq_to_desc() while
holding rcu read lock, since desc and desc->kstat_irqs wont disappear or
change.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Link: https://lkml.kernel.org/r/20180620150332.163320-1-edumazet@google.com
parent 0a13ec0b

kernel/irq/proc.c

+12 −10
Original line number Diff line number Diff line
@@ -475,22 +475,24 @@ int show_interrupts(struct seq_file *p, void *v) 
		seq_putc(p, '\n');

	}



	irq_lock_sparse();

	rcu_read_lock();

	desc = irq_to_desc(i);

	if (!desc)

		goto outsparse;



	raw_spin_lock_irqsave(&desc->lock, flags);

	if (desc->kstat_irqs)

		for_each_online_cpu(j)

		any_count |= kstat_irqs_cpu(i, j);

	action = desc->action;

	if ((!action || irq_desc_is_chained(desc)) && !any_count)

		goto out;

			any_count |= *per_cpu_ptr(desc->kstat_irqs, j);



	if ((!desc->action || irq_desc_is_chained(desc)) && !any_count)

		goto outsparse;



	seq_printf(p, "%*d: ", prec, i);

	for_each_online_cpu(j)

		seq_printf(p, "%10u ", kstat_irqs_cpu(i, j));

		seq_printf(p, "%10u ", desc->kstat_irqs ?

					*per_cpu_ptr(desc->kstat_irqs, j) : 0);



	raw_spin_lock_irqsave(&desc->lock, flags);

	if (desc->irq_data.chip) {

		if (desc->irq_data.chip->irq_print_chip)

			desc->irq_data.chip->irq_print_chip(&desc->irq_data, p);
@@ -511,6 +513,7 @@ int show_interrupts(struct seq_file *p, void *v) 
	if (desc->name)

		seq_printf(p, "-%-8s", desc->name);



	action = desc->action;

	if (action) {

		seq_printf(p, "  %s", action->name);

		while ((action = action->next) != NULL)
@@ -518,10 +521,9 @@ int show_interrupts(struct seq_file *p, void *v) 
	}



	seq_putc(p, '\n');

out:

	raw_spin_unlock_irqrestore(&desc->lock, flags);

outsparse:

	irq_unlock_sparse();

	rcu_read_unlock();

	return 0;

}

#endif