Re: [PATCH 05/15] s390/time: Prepare to stop elapsing in dynticks-idle
From: Heiko Carstens <hca@linux.ibm.com>
Date: 2026-01-21 12:18:39
Also in:
linux-pm, linux-s390, lkml
Subsystem:
s390 architecture, the rest · Maintainers:
Heiko Carstens, Vasily Gorbik, Alexander Gordeev, Linus Torvalds
On Fri, Jan 16, 2026 at 03:51:58PM +0100, Frederic Weisbecker wrote:
quoted hunk ↗ jump to hunk
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) {