Visa, tech@,

in my work to bring support queues in cnmac I think I discovered a weird
issue in interrupts and barrier in octeon.

octciu_intr_establish() has:

   201          int cpuid = cpu_number();
...
   208  #ifdef MULTIPROCESSOR
   209          /* Span work queue interrupts across CPUs. */
   210          if (IS_WORKQ_IRQ(irq))
   211                  cpuid = irq % ncpus;
   212  #endif
...
   222          ih->ih_irq = irq;

my understanding is that octciu_intr_establish() happens on autoconf where
only CPU0 exists, and on octeon we increase ncpus in cpu hatch, and not
attach, which means that ncpus is 1 at octciu_intr_establish() time.

What makes cpuid always 1 for that code and schedules all interrupts on
CPU0.

Next, octciu_intr_barrier():

   290  void
   291  octciu_intr_barrier(void *_ih)
   292  {
   293          struct cpu_info *ci = NULL;
   294  #ifdef MULTIPROCESSOR
   295          struct octciu_intrhand *ih = _ih;
      
   296          if (IS_WORKQ_IRQ(ih->ih_irq))
   297                  ci = get_cpu_info(ih->ih_irq % ncpus);
   298  #endif
      
   299          sched_barrier(ci);
   300  }

because ih->ih_irq is 0 here, it picks cpu0 only.

kn@'s diff https://marc.info/?l=openbsd-bugs&m=177171071006897&w=2
introduced a regression on my ER-4:
https://marc.info/?l=openbsd-bugs&m=177177669428825&w=2 and this regression
can be avoided by removing the block in octciu_intr_establish().

Here is the diff where I remove this block and % ncpus.

This diff keeps interrupts on CPU0 which is, actually, current behaviour and
unblocks kn@'s diff to enable softnet threads on octeon which unblocks my
work of making cnmac with RX queue:
https://marc.info/?l=openbsd-tech&m=177506394121597&w=2

So far I see this diff as safe because it doesn't change current behaviour
but I may miss some details.

OK to commit it?

Index: sys/arch/octeon/dev/octciu.c
===================================================================
RCS file: /home/cvs/src/sys/arch/octeon/dev/octciu.c,v
diff -u -p -r1.19 octciu.c
--- sys/arch/octeon/dev/octciu.c	11 Dec 2022 05:31:05 -0000	1.19
+++ sys/arch/octeon/dev/octciu.c	1 Apr 2026 19:39:40 -0000
@@ -250,12 +250,6 @@ octciu_intr_establish(int irq, int level
 		panic("%s: illegal irq %d", __func__, irq);
 #endif
 
-#ifdef MULTIPROCESSOR
-	/* Span work queue interrupts across CPUs. */
-	if (IS_WORKQ_IRQ(irq))
-		cpuid = irq % ncpus;
-#endif
-
 	flags = (level & IPL_MPSAFE) ? CIH_MPSAFE : 0;
 	level &= ~IPL_MPSAFE;
 
@@ -363,7 +357,7 @@ octciu_intr_barrier(void *_ih)
 	struct octciu_intrhand *ih = _ih;
 
 	if (IS_WORKQ_IRQ(ih->ih_irq))
-		ci = get_cpu_info(ih->ih_irq % ncpus);
+		ci = get_cpu_info(ih->ih_irq);
 #endif
 
 	sched_barrier(ci);


-- 
wbr, Kirill