On Fri, Jan 16, 2026 at 03:51:58PM +0100, Frederic Weisbecker wrote:
> diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
> index 39cb8d0ae348..54bb932184dd 100644
> --- a/arch/s390/kernel/idle.c
> +++ b/arch/s390/kernel/idle.c
> @@ -35,6 +35,12 @@ void account_idle_time_irq(void)
> this_cpu_add(mt_cycles[i], cycles_new[i] -
> idle->mt_cycles_enter[i]);
> }
>
> + WRITE_ONCE(idle->idle_count, READ_ONCE(idle->idle_count) + 1);
> +
> + /* Dyntick idle time accounted by nohz/scheduler */
> + if (idle->idle_dyntick)
> + return;
> +
> idle_time = lc->int_clock - idle->clock_idle_enter;
>
> lc->steal_timer += idle->clock_idle_enter - lc->last_update_clock;
> @@ -45,7 +51,6 @@ void account_idle_time_irq(void)
>
> /* Account time spent with enabled wait psw loaded as idle time. */
> WRITE_ONCE(idle->idle_time, READ_ONCE(idle->idle_time) + idle_time);
> - WRITE_ONCE(idle->idle_count, READ_ONCE(idle->idle_count) + 1);
> account_idle_time(cputime_to_nsecs(idle_time));
> }
This breaks idle time reporting (aka enabled wait psw time) via the per-cpu
sysfs files (see show_idle_time()). That is: the second WRITE_ONCE() should
also go above the early return statement; but of course this leads to other
dependencies...
Not sure what to do with this. I thought about removing those sysfs files
already in the past, since they are of very limited use; and most likely
nothing in user space would miss them.
Anyway, you need to integrate the trivial patch below, so everything compiles
for s390. It also _seems_ to work.
Guess I need to spend some more time on accounting and see what it would take
to convert to VIRT_CPU_ACCOUNTING_GEN, while keeping the current precision and
functionality.
diff --git a/arch/s390/include/asm/idle.h b/arch/s390/include/asm/idle.h
index 2770c4f761e1..285b3da318d6 100644
--- a/arch/s390/include/asm/idle.h
+++ b/arch/s390/include/asm/idle.h
@@ -8,6 +8,7 @@
#ifndef _S390_IDLE_H
#define _S390_IDLE_H
+#include <linux/percpu-defs.h>
#include <linux/types.h>
#include <linux/device.h>
@@ -20,6 +21,8 @@ struct s390_idle_data {
unsigned long mt_cycles_enter[8];
};
+DECLARE_PER_CPU(struct s390_idle_data, s390_idle);
+
extern struct device_attribute dev_attr_idle_count;
extern struct device_attribute dev_attr_idle_time_us;
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index 54bb932184dd..e3fe64e7adbe 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -19,7 +19,7 @@
#include <asm/smp.h>
#include "entry.h"
-static DEFINE_PER_CPU(struct s390_idle_data, s390_idle);
+DEFINE_PER_CPU(struct s390_idle_data, s390_idle);
void account_idle_time_irq(void)
{
