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Message-ID: <20260116145208.87445-5-frederic@kernel.org>
Date: Fri, 16 Jan 2026 15:51:57 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Alexander Gordeev <agordeev@...ux.ibm.com>,
Anna-Maria Behnsen <anna-maria@...utronix.de>,
Ben Segall <bsegall@...gle.com>,
Boqun Feng <boqun.feng@...il.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Heiko Carstens <hca@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>,
Jan Kiszka <jan.kiszka@...mens.com>,
Joel Fernandes <joelagnelf@...dia.com>,
Juri Lelli <juri.lelli@...hat.com>,
Kieran Bingham <kbingham@...nel.org>,
Madhavan Srinivasan <maddy@...ux.ibm.com>,
Mel Gorman <mgorman@...e.de>,
Michael Ellerman <mpe@...erman.id.au>,
Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
Nicholas Piggin <npiggin@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Sven Schnelle <svens@...ux.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Uladzislau Rezki <urezki@...il.com>,
Valentin Schneider <vschneid@...hat.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Viresh Kumar <viresh.kumar@...aro.org>,
Xin Zhao <jackzxcui1989@....com>,
linux-pm@...r.kernel.org,
linux-s390@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 04/15] powerpc/time: Prepare to stop elapsing in dynticks-idle
Currently the tick subsystem stores the idle cputime accounting in
private fields, allowing cohabitation with architecture idle vtime
accounting. The former is fetched on online CPUs, the latter on offline
CPUs.
For consolidation purpose, architecture vtime accounting will continue
to account the cputime but will make a break when the idle tick is
stopped. The dyntick cputime accounting will then be relayed by the tick
subsystem so that the idle cputime is still seen advancing coherently
even when the tick isn't there to flush the idle vtime.
Prepare for that and introduce three new APIs which will be used in
subsequent patches:
_ vtime_dynticks_start() is deemed to be called when idle enters in
dyntick mode. The idle cputime that elapsed so far is accumulated.
- vtime_dynticks_stop() is deemed to be called when idle exits from
dyntick mode. The vtime entry clocks are fast-forward to current time
so that idle accounting restarts elapsing from now.
- vtime_reset() is deemed to be called from dynticks idle IRQ entry to
fast-forward the clock to current time so that the IRQ time is still
accounted by vtime while nohz cputime is paused.
Also accumulated vtime won't be flushed from dyntick-idle ticks to avoid
accounting twice the idle cputime, along with nohz accounting.
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
arch/powerpc/kernel/time.c | 41 ++++++++++++++++++++++++++++++++++++++
include/linux/vtime.h | 6 ++++++
2 files changed, 47 insertions(+)
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 4bbeb8644d3d..9b3167274653 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -376,6 +376,47 @@ void vtime_task_switch(struct task_struct *prev)
acct->starttime = acct0->starttime;
}
}
+
+#ifdef CONFIG_NO_HZ_COMMON
+/**
+ * vtime_reset - Fast forward vtime entry clocks
+ *
+ * Called from dynticks idle IRQ entry to fast-forward the clocks to current time
+ * so that the IRQ time is still accounted by vtime while nohz cputime is paused.
+ */
+void vtime_reset(void)
+{
+ struct cpu_accounting_data *acct = get_accounting(current);
+
+ acct->starttime = mftb();
+#ifdef CONFIG_ARCH_HAS_SCALED_CPUTIME
+ acct->startspurr = read_spurr(now);
+#endif
+}
+
+/**
+ * vtime_dyntick_start - Inform vtime about entry to idle-dynticks
+ *
+ * Called when idle enters in dyntick mode. The idle cputime that elapsed so far
+ * is accumulated and the tick subsystem takes over the idle cputime accounting.
+ */
+void vtime_dyntick_start(void)
+{
+ vtime_account_idle(current);
+}
+
+/**
+ * vtime_dyntick_stop - Inform vtime about exit from idle-dynticks
+ *
+ * Called when idle exits from dyntick mode. The vtime entry clocks are
+ * fast-forward to current time so that idle accounting restarts elapsing from
+ * now.
+ */
+void vtime_dyntick_stop(void)
+{
+ vtime_reset();
+}
+#endif /* CONFIG_NO_HZ_COMMON */
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
void __no_kcsan __delay(unsigned long loops)
diff --git a/include/linux/vtime.h b/include/linux/vtime.h
index 737930f66c3e..10cdb08f960b 100644
--- a/include/linux/vtime.h
+++ b/include/linux/vtime.h
@@ -37,11 +37,17 @@ extern void vtime_account_irq(struct task_struct *tsk, unsigned int offset);
extern void vtime_account_softirq(struct task_struct *tsk);
extern void vtime_account_hardirq(struct task_struct *tsk);
extern void vtime_flush(struct task_struct *tsk);
+extern void vtime_reset(void);
+extern void vtime_dyntick_start(void);
+extern void vtime_dyntick_stop(void);
#else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
static inline void vtime_account_irq(struct task_struct *tsk, unsigned int offset) { }
static inline void vtime_account_softirq(struct task_struct *tsk) { }
static inline void vtime_account_hardirq(struct task_struct *tsk) { }
static inline void vtime_flush(struct task_struct *tsk) { }
+static inline void vtime_reset(void) { }
+static inline void vtime_dyntick_start(void) { }
+extern inline void vtime_dyntick_stop(void) { }
#endif
/*
--
2.51.1
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