[PATCHv10 3/4] genirq: Avoid summation loops for /proc/interrupts

[Bitao Hu]

We could use the irq_desc::tot_count member to avoid the summation
loop for interrupts which are not marked as 'PER_CPU' interrupts in
'show_interrupts'. This could reduce the time overhead of reading
/proc/interrupts.

Originally-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Bitao Hu <yaoma@xxxxxxxxxxxxxxxxx>
---
 include/linux/irqdesc.h | 2 ++
 kernel/irq/irqdesc.c    | 2 +-
 kernel/irq/proc.c       | 9 +++++++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index 2912b1998670..1ee96d7232b4 100644
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -121,6 +121,8 @@ static inline void irq_unlock_sparse(void) { }
 extern struct irq_desc irq_desc[NR_IRQS];
 #endif
 
+extern bool irq_is_nmi(struct irq_desc *desc);
+
 static inline unsigned int irq_desc_kstat_cpu(struct irq_desc *desc,
 					      unsigned int cpu)
 {
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index 9cd17080b2d8..56a767957a9d 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -955,7 +955,7 @@ unsigned int kstat_irqs_cpu(unsigned int irq, int cpu)
 	return desc && desc->kstat_irqs ? per_cpu(desc->kstat_irqs->cnt, cpu) : 0;
 }
 
-static bool irq_is_nmi(struct irq_desc *desc)
+bool irq_is_nmi(struct irq_desc *desc)
 {
 	return desc->istate & IRQS_NMI;
 }
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 6954e0a02047..b3b1b93f0410 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -489,8 +489,13 @@ int show_interrupts(struct seq_file *p, void *v)
 		goto outsparse;
 
 	if (desc->kstat_irqs) {
-		for_each_online_cpu(j)
-			any_count |= data_race(per_cpu(desc->kstat_irqs->cnt, j));
+		if (!irq_settings_is_per_cpu_devid(desc) &&
+		    !irq_settings_is_per_cpu(desc) &&
+		    !irq_is_nmi(desc))
+			any_count = data_race(desc->tot_count);
+		else
+			for_each_online_cpu(j)
+				any_count |= data_race(per_cpu(desc->kstat_irqs->cnt, j));
 	}
 
 	if ((!desc->action || irq_desc_is_chained(desc)) && !any_count)
-- 
2.37.1 (Apple Git-137.1)