[patch 13/14] [RFC] genirq/proc: Provide architecture specific binary statistics

[Thomas Gleixner <tglx@kernel.org>]

Provide a binary statistics interface similar to the per device and per CPU
interfaces to access the architecture specific interrupt statistics.

The architecture has to select it in Kconfig and provide an accessor to the
per CPU interrupt information and the number of architecture specific
entries.

The entries are ordered by a numerical index starting from 0, which
corresponds to the ordering of those interrupts in /proc/interrupt. The
output format is the same as for the per device and per CPU interfaces and
only contains entries which have an interrupt count > 0.

Reading the architecture specific counters of a 256 CPU x86 system takes
36us kernel time for 6 interrupts with non-zero counts and produces about
10k of data.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
---
 kernel/irq/Kconfig |    3 ++
 kernel/irq/proc.c  |   56 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -18,6 +18,9 @@ config GENERIC_IRQ_SHOW
 config GENERIC_IRQ_SHOW_LEVEL
        bool
 
+config GENERIC_IRQ_STATS_ARCH
+       bool
+
 config GENERIC_IRQ_STATS_PERCPU
        bool
 
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -945,6 +945,61 @@ static __init void irq_pcp_stats_init(vo
 static inline void irq_pcp_stats_init(void) { }
 #endif /* !CONFIG_GENERIC_IRQ_STATS_PERCPU */
 
+#ifdef CONFIG_GENERIC_IRQ_STATS_ARCH
+static inline void arch_stat_update_one(struct irq_proc_stat *s)
+{
+	struct irq_proc_stat_data *d = s->data;
+	unsigned int cpu, idx = s->irqnr;
+
+	for_each_online_cpu(cpu) {
+		struct irq_proc_stat_cpu pcpu = {
+			.cpu = cpu,
+			.cnt = arch_get_irq_stat(cpu, idx),
+		};
+
+		if (pcpu.cnt)
+			d->pcpu[d->entries++] = pcpu;
+	}
+
+	if (d->entries) {
+		d->irqnr = idx;
+		s->count = sizeof(*d) + d->entries * sizeof(*d->pcpu);
+	}
+}
+
+static __always_inline bool arch_stat_next_data(struct irq_proc_stat *s)
+{
+	if (unlikely(s->first)) {
+		s->irqnr = 0;
+		s->first = false;
+	}
+
+	for(; !s->count && s->irqnr < ARCH_IRQ_STATS_NUM_IRQS; s->irqnr++)
+		arch_stat_update_one(s);
+	return !!s->count;
+}
+
+static ssize_t irq_arch_stats_read(struct kiocb *iocb, struct iov_iter *iter)
+{
+	return __irq_stats_read(iocb, iter, arch_stat_next_data);
+}
+
+static const struct proc_ops irq_arch_stat_ops = {
+	.proc_flags	= PROC_ENTRY_PERMANENT,
+	.proc_open	= irq_stats_open,
+	.proc_release	= irq_stats_release,
+	.proc_read_iter	= irq_arch_stats_read,
+	.proc_lseek	= irq_stats_llseek,
+};
+
+static __init void irq_arch_stats_init(void)
+{
+	proc_create("arch_stats", 0, root_irq_dir, &irq_arch_stat_ops);
+}
+#else  /* CONFIG_GENERIC_IRQ_STATS_ARCH */
+static inline void irq_arch_stats_init(void) { }
+#endif /* !CONFIG_GENERIC_IRQ_STATS_ARCH */
+
 static int __init irq_proc_init(void)
 {
 	proc_create_seq("interrupts", 0, NULL, &irq_seq_ops);
@@ -953,6 +1008,7 @@ static int __init irq_proc_init(void)
 
 	proc_create("device_stats", 0, root_irq_dir, &irq_dev_stat_ops);
 	irq_pcp_stats_init();
+	irq_arch_stats_init();
 	return 0;
 }
 fs_initcall(irq_proc_init);