[patch V3 10/14] genirq: Calculate precision only when required

[Thomas Gleixner <tglx@kernel.org>]

Calculating the precision of the interrupt number column on every initial
show_interrupt() invocation is a pointless exercise as the underlying
maximum number of interrupts rarely changes.

Calculate it only when that number is modified and let show_interrupts()
use the cached value.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
Reviewed-by: Radu Rendec <radu@rendec.net>
---
 kernel/irq/internals.h |    6 ++++++
 kernel/irq/irqdesc.c   |   10 ++++++----
 kernel/irq/proc.c      |   33 +++++++++++++++++++++++----------
 3 files changed, 35 insertions(+), 14 deletions(-)

--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -134,6 +134,12 @@ static inline void unregister_handler_pr
 static inline void irq_proc_update_valid(struct irq_desc *desc) { }
 #endif
 
+#if defined(CONFIG_PROC_FS) && defined(CONFIG_GENERIC_IRQ_SHOW)
+void irq_proc_calc_prec(void);
+#else
+static inline void irq_proc_calc_prec(void) { }
+#endif
+
 extern bool irq_can_set_affinity_usr(unsigned int irq);
 
 extern int irq_do_set_affinity(struct irq_data *data,
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -157,13 +157,12 @@ EXPORT_SYMBOL_GPL(irq_get_nr_irqs);
  *
  * Return: @nr.
  */
-unsigned int irq_set_nr_irqs(unsigned int nr)
+unsigned int __init irq_set_nr_irqs(unsigned int nr)
 {
 	total_nr_irqs = nr;
-
+	irq_proc_calc_prec();
 	return nr;
 }
-EXPORT_SYMBOL_GPL(irq_set_nr_irqs);
 
 static DEFINE_MUTEX(sparse_irq_lock);
 static struct maple_tree sparse_irqs = MTREE_INIT_EXT(sparse_irqs,
@@ -544,6 +543,7 @@ static bool irq_expand_nr_irqs(unsigned
 	if (nr > MAX_SPARSE_IRQS)
 		return false;
 	total_nr_irqs = nr;
+	irq_proc_calc_prec();
 	return true;
 }
 
@@ -572,6 +572,7 @@ int __init early_irq_init(void)
 		desc = alloc_desc(i, node, 0, NULL, NULL);
 		irq_insert_desc(i, desc);
 	}
+	irq_proc_calc_prec();
 	return arch_early_irq_init();
 }
 
@@ -592,7 +593,7 @@ int __init early_irq_init(void)
 
 	init_irq_default_affinity();
 
-	printk(KERN_INFO "NR_IRQS: %d\n", NR_IRQS);
+	pr_info("NR_IRQS: %d\n", NR_IRQS);
 
 	count = ARRAY_SIZE(irq_desc);
 
@@ -602,6 +603,7 @@ int __init early_irq_init(void)
 			goto __free_desc_res;
 	}
 
+	irq_proc_calc_prec();
 	return arch_early_irq_init();
 
 __free_desc_res:
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -456,10 +456,25 @@ int __weak arch_show_interrupts(struct s
 	return 0;
 }
 
+static struct irq_proc_constraints {
+	unsigned int	num_prec;
+} irq_proc_constraints __read_mostly = {
+	.num_prec	= 3,
+};
+
 #ifndef ACTUAL_NR_IRQS
 # define ACTUAL_NR_IRQS total_nr_irqs
 #endif
 
+void irq_proc_calc_prec(void)
+{
+	unsigned int prec, n;
+
+	for (prec = 3, n = 1000; prec < 10 && n <= total_nr_irqs; ++prec)
+		n *= 10;
+	WRITE_ONCE(irq_proc_constraints.num_prec, prec);
+}
+
 #define ZSTR1 "          0"
 #define ZSTR1_LEN	(sizeof(ZSTR1) - 1)
 #define ZSTR16		ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 ZSTR1 \
@@ -498,9 +513,7 @@ void irq_proc_emit_counts(struct seq_fil
 
 int show_interrupts(struct seq_file *p, void *v)
 {
-	const unsigned int nr_irqs = total_nr_irqs;
-	static int prec;
-
+	unsigned int prec = READ_ONCE(irq_proc_constraints.num_prec);
 	int i = *(loff_t *) v, j;
 	struct irqaction *action;
 	struct irq_desc *desc;
@@ -513,9 +526,6 @@ int show_interrupts(struct seq_file *p,
 
 	/* print header and calculate the width of the first column */
 	if (i == 0) {
-		for (prec = 3, j = 1000; prec < 10 && j <= nr_irqs; ++prec)
-			j *= 10;
-
 		seq_printf(p, "%*s", prec + 8, "");
 		for_each_online_cpu(j)
 			seq_printf(p, "CPU%-8d", j);
@@ -551,13 +561,16 @@ int show_interrupts(struct seq_file *p,
 	} else {
 		seq_printf(p, "%8s", "None");
 	}
+
+	seq_putc(p, ' ');
 	if (desc->irq_data.domain)
-		seq_printf(p, " %*lu", prec, desc->irq_data.hwirq);
+		seq_put_decimal_ull_width(p, "", desc->irq_data.hwirq, prec);
 	else
 		seq_printf(p, " %*s", prec, "");
-#ifdef CONFIG_GENERIC_IRQ_SHOW_LEVEL
-	seq_printf(p, " %-8s", irqd_is_level_type(&desc->irq_data) ? "Level" : "Edge");
-#endif
+
+	if (IS_ENABLED(CONFIG_GENERIC_IRQ_SHOW_LEVEL))
+		seq_printf(p, " %-8s", irqd_is_level_type(&desc->irq_data) ? "Level" : "Edge");
+
 	if (desc->name)
 		seq_printf(p, "-%-8s", desc->name);