genirq/proc: Utilize irq_desc::tot_count to avoid evaluation

Interrupts which are not marked per CPU increment not only the per CPU
statistics, but also the accumulation counter irq_desc::tot_count.

Change the counter to type unsigned long so it does not produce sporadic
zeros due to wrap arounds on 64-bit machines and do a quick check for non
per CPU interrupts. If the counter is zero, then simply emit a full set of
zero strings. That spares the evaluation of the per CPU counters completely
for interrupts with zero events.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
Reviewed-by: Radu Rendec <radu@rendec.net>
Link: https://patch.msgid.link/20260517194931.115522199@kernel.org

diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
index dae9a9b936651b22d21ee42ce2ea9fe0a56b9aff..1058786d76ebb353ed59cb00fff56616a5202792 100644 (file)
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -52,8 +52,8 @@ struct irq_redirect {
  * @depth:             disable-depth, for nested irq_disable() calls
  * @wake_depth:                enable depth, for multiple irq_set_irq_wake() callers
  * @tot_count:         stats field for non-percpu irqs
- * @irq_count:         stats field to detect stalled irqs
  * @last_unhandled:    aging timer for unhandled count
+ * @irq_count:         stats field to detect stalled irqs
  * @irqs_unhandled:    stats field for spurious unhandled interrupts
  * @threads_handled:   stats field for deferred spurious detection of threaded handlers
  * @threads_handled_last: comparator field for deferred spurious detection of threaded handlers
@@ -87,9 +87,9 @@ struct irq_desc {
        unsigned int            core_internal_state__do_not_mess_with_it;
        unsigned int            depth;          /* nested irq disables */
        unsigned int            wake_depth;     /* nested wake enables */
-       unsigned int            tot_count;
-       unsigned int            irq_count;      /* For detecting broken IRQs */
+       unsigned long           tot_count;
        unsigned long           last_unhandled; /* Aging timer for unhandled count */
+       unsigned int            irq_count;      /* For detecting broken IRQs */
        unsigned int            irqs_unhandled;
        atomic_t                threads_handled;
        int                     threads_handled_last;

diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 378b523a1b00bd2e949df77d86e155fa76745ae2..5a1805b0b8a9d06e43d53bab121404e3b617370a 100644 (file)
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -523,7 +523,16 @@ int show_interrupts(struct seq_file *p, void *v)
                return 0;
 
        seq_printf(p, "%*d:", prec, i);
-       irq_proc_emit_counts(p, &desc->kstat_irqs->cnt);
+
+       /*
+        * Always output per CPU interrupts. Output device interrupts only when
+        * desc::tot_count is not zero.
+        */
+       if (irq_settings_is_per_cpu(desc) || irq_settings_is_per_cpu_devid(desc) ||
+           data_race(desc->tot_count))
+               irq_proc_emit_counts(p, &desc->kstat_irqs->cnt);
+       else
+               irq_proc_emit_zero_counts(p, num_online_cpus());
        seq_putc(p, ' ');
 
        guard(raw_spinlock_irq)(&desc->lock);