[patch V4 10/15] genirq: Cache the condition for /proc/interrupts exposure

Thomas Gleixner
2026-03-31T07:26:19Z

show_interrupts() evaluates a boatload of conditions to establish whether
it should expose an interrupt in /proc/interrupts or not.

That can be simplified by caching the condition in an internal status flag,
which is updated when one of the relevant inputs changes.

The irq_desc::kstat_irq check is dropped because visible interrupt
descriptors always have a valid pointer.

As a result the number of instructions and branches for reading
/proc/interrupts is reduced significantly.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
---
V4: Cover freeing of per CPU and NMI type interrupts
V3: Remove the historical kstat_irq check - Radu
V2: s/IRQF_/IRQ/ and fixup the enum treatment - Dmitry
---
include/linux/irq.h | 1 +
kernel/irq/chip.c | 2 ++
kernel/irq/internals.h | 2 ++
kernel/irq/manage.c | 9 ++++++++-
kernel/irq/proc.c | 15 +++++++++++----
kernel/irq/settings.h | 13 +++++++++++++
6 files changed, 37 insertions(+), 5 deletions(-)
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -99,6 +99,7 @@ enum {
IRQ_DISABLE_UNLAZY = (1 << 19),
IRQ_HIDDEN = (1 << 20),
IRQ_NO_DEBUG = (1 << 21),
+ IRQ_RESERVED = (1 << 22),
};

#define IRQF_MODIFY_MASK \
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -1004,6 +1004,7 @@ static void
WARN_ON(irq_chip_pm_get(irq_desc_get_irq_data(desc)));
irq_activate_and_startup(desc, IRQ_RESEND);
}
+ irq_proc_update_valid(desc);
}

void __irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
@@ -1064,6 +1065,7 @@ void irq_modify_status(unsigned int irq,
trigger = tmp;

irqd_set(&desc->irq_data, trigger);
+ irq_proc_update_valid(desc);
}
}
EXPORT_SYMBOL_GPL(irq_modify_status);
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -123,6 +123,7 @@ extern void register_irq_proc(unsigned i
extern void unregister_irq_proc(unsigned int irq, struct irq_desc *desc);
extern void register_handler_proc(unsigned int irq, struct irqaction *action);
extern void unregister_handler_proc(unsigned int irq, struct irqaction *action);
+void irq_proc_update_valid(struct irq_desc *desc);
#else
static inline void register_irq_proc(unsigned int irq, struct irq_desc *desc) { }
static inline void unregister_irq_proc(unsigned int irq, struct irq_desc *desc) { }
@@ -130,6 +131,7 @@ static inline void register_handler_proc
struct irqaction *action) { }
static inline void unregister_handler_proc(unsigned int irq,
struct irqaction *action) { }
+static inline void irq_proc_update_valid(struct irq_desc *desc) { }
#endif

extern bool irq_can_set_affinity_usr(unsigned int irq);
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1802,6 +1802,7 @@ static int
__enable_irq(desc);
}

+ irq_proc_update_valid(desc);
raw_spin_unlock_irqrestore(&desc->lock, flags);
chip_bus_sync_unlock(desc);
mutex_unlock(&desc->request_mutex);
@@ -1906,6 +1907,7 @@ static struct irqaction *__free_irq(stru
desc->affinity_hint = NULL;
#endif

+ irq_proc_update_valid(desc);
raw_spin_unlock_irqrestore(&desc->lock, flags);
/*
* Drop bus_lock here so the changes which were done in the chip
@@ -2047,6 +2049,8 @@ static const void *__cleanup_nmi(unsigne
irq_shutdown_and_deactivate(desc);
}

+ irq_proc_update_valid(desc);
+
if (action)
unregister_handler_proc(irq, action);
kfree(action);
@@ -2062,6 +2066,7 @@ static const void *__cleanup_nmi(unsigne
const void *free_nmi(unsigned int irq, void *dev_id)
{
struct irq_desc *desc = irq_to_desc(irq);
+ void *ret;

if (!desc || WARN_ON(!irq_is_nmi(desc)))
return NULL;
@@ -2433,8 +2438,10 @@ static struct irqaction *__free_percpu_i
*action_ptr = action->next;

/* Demote from NMI if we killed the last action */
- if (!desc->action)
+ if (!desc->action) {
desc->istate &= ~IRQS_NMI;
+ irq_proc_update_valid(desc);
+ }
}

unregister_handler_proc(irq, action);
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -439,6 +439,16 @@ void init_irq_proc(void)
register_irq_proc(irq, desc);
}

+void irq_proc_update_valid(struct irq_desc *desc)
+{
+ u32 set = _IRQ_PROC_VALID;
+
+ if (irq_settings_is_hidden(desc) || irq_desc_is_chained(desc) || !desc->action)
+ set = 0;
+
+ irq_settings_update_proc_valid(desc, set);
+}
+
#ifdef CONFIG_GENERIC_IRQ_SHOW

int __weak arch_show_interrupts(struct seq_file *p, int prec)
@@ -514,10 +524,7 @@ int show_interrupts(struct seq_file *p,

guard(rcu)();
desc = irq_to_desc(i);
- if (!desc || irq_settings_is_hidden(desc))
- return 0;
-
- if (!desc->action || irq_desc_is_chained(desc) || !desc->kstat_irqs)
+ if (!desc || !irq_settings_proc_valid(desc))
return 0;

seq_printf(p, "%*d:", prec, i);
--- a/kernel/irq/settings.h
+++ b/kernel/irq/settings.h
@@ -18,6 +18,7 @@ enum {
_IRQ_DISABLE_UNLAZY = IRQ_DISABLE_UNLAZY,
_IRQ_HIDDEN = IRQ_HIDDEN,
_IRQ_NO_DEBUG = IRQ_NO_DEBUG,
+ _IRQ_PROC_VALID = IRQ_RESERVED,
_IRQF_MODIFY_MASK = IRQF_MODIFY_MASK,
};

@@ -34,6 +35,7 @@ enum {
#define IRQ_DISABLE_UNLAZY GOT_YOU_MORON
#define IRQ_HIDDEN GOT_YOU_MORON
#define IRQ_NO_DEBUG GOT_YOU_MORON
+#define IRQ_RESERVED GOT_YOU_MORON
#undef IRQF_MODIFY_MASK
#define IRQF_MODIFY_MASK GOT_YOU_MORON

@@ -180,3 +182,14 @@ static inline bool irq_settings_no_debug
{
return desc->status_use_accessors & _IRQ_NO_DEBUG;
}
+
+static inline bool irq_settings_proc_valid(struct irq_desc *desc)
+{
+ return desc->status_use_accessors & _IRQ_PROC_VALID;
+}
+
+static inline void irq_settings_update_proc_valid(struct irq_desc *desc, u32 set)
+{
+ desc->status_use_accessors &= ~_IRQ_PROC_VALID;
+ desc->status_use_accessors |= (set & _IRQ_PROC_VALID);
+}