linux-kernel - Re: [PATCH 01/15] sched/idle: Handle offlining first in idle loop

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Message-ID: <aW-WoBsdb-jKDomL@localhost.localdomain>
Date: Tue, 20 Jan 2026 15:52:16 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.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>,
	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: Re: [PATCH 01/15] sched/idle: Handle offlining first in idle loop

Le Tue, Jan 20, 2026 at 09:56:12AM +0530, K Prateek Nayak a écrit :
> Hello Frederic, Peter,
> 
> On 1/20/2026 2:34 AM, Frederic Weisbecker wrote:
> > Le Mon, Jan 19, 2026 at 01:53:47PM +0100, Peter Zijlstra a écrit :
> >> On Fri, Jan 16, 2026 at 03:51:54PM +0100, Frederic Weisbecker wrote:
> >>
> >>>  kernel/sched/idle.c | 11 ++++++-----
> >>>  1 file changed, 6 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> >>> index c174afe1dd17..35d79af3286d 100644
> >>> --- a/kernel/sched/idle.c
> >>> +++ b/kernel/sched/idle.c
> >>> @@ -260,6 +260,12 @@ static void do_idle(void)
> >>>  {
> >>>  	int cpu = smp_processor_id();
> >>>  
> >>> +	if (cpu_is_offline(cpu)) {
> >>
> >> Does it make sense to make that: if (unlikely(cpu_is_offline(cpu))) ?
> > 
> > Yes indeed!
> 
> nit. but don't we inherit it from:
> 
> #define cpu_is_offline(cpu)     unlikely(!cpu_online(cpu))
> 
> so it will end up being annotated with unlikely() no?

Ah right!

> 
> -- 
> Thanks and Regards,
> Prateek
> 

-- 
Frederic Weisbecker
SUSE Labs