From nobody Mon Feb 9 04:29:30 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90E523EFD3D; Fri, 6 Feb 2026 14:23:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770387785; cv=none; b=Kt74/rDbvI73T3ZZCAc4IDjFZ6IMWALwR5CnYLi3OeTRAIR95WGTkGFE7GNxtS1xd88NdEbHDpnu9qBY6H528tU8Y5bpCqsiY/Y6Jo9debIUG6jbSW2mAwkHTLag1eVdt0g9rxM4yKL61/BBOSdlwpiRfZtIEqLpBOHgsq/px6o= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770387785; c=relaxed/simple; bh=wLAGVyuXhhrWKSeELGYkoOFpqB5ysD0I9rHCulvW2nY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=uX5dxLDGmJSb6b2eVaX6OclAqqZVkXVt5YnFQHWpfn1DIOGxj3Ou8HZKUmXkFdZM5B362052ONrgd7OwX9hx8EPDTyW6Q7IRFrqxKrLRwZaOhPiVfalPO96fIQe+seqZVsASa9jrKM6JXALPcyG46dLYWw1fpnQu33VxOVHISSM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JpZ8uh3d; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JpZ8uh3d" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B52E9C19422; Fri, 6 Feb 2026 14:22:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770387785; bh=wLAGVyuXhhrWKSeELGYkoOFpqB5ysD0I9rHCulvW2nY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=JpZ8uh3dVO70F+77got86Wunt3Up/fK/qFnnYDGHTtdQmqrjOvVd3KVzTRYvBu0y+ hdptMlW1CyrwZUjMxaknor8oyK3IRqdqjaqtM22j0CKyPl24pF+YtrXA7/ywoUsqVc N9FX/G/KlvtZP8UxRFrnyUBU06Yv5WyoSVVEeBxk/62132uvMF9T6F+EG0VdunYtzv rnhxjkXAi7wdshbMhVW+Nut7nB0ETScRmNlE8rJMSW5BA8jxbGhTLWuoA+ffTzdJxY eKxCztC7aCrqJmnr9bEPApU27MVgTDBeostanKewHhWrIQeSoqcWzG7/MaOwP3EPwu wQo4EUCnj7jcg== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , "Christophe Leroy (CS GROUP)" , "Rafael J. Wysocki" , Alexander Gordeev , Anna-Maria Behnsen , Ben Segall , Boqun Feng , Christian Borntraeger , Dietmar Eggemann , Heiko Carstens , Ingo Molnar , Jan Kiszka , Joel Fernandes , Juri Lelli , Kieran Bingham , Madhavan Srinivasan , Mel Gorman , Michael Ellerman , Neeraj Upadhyay , Nicholas Piggin , "Paul E . McKenney" , Peter Zijlstra , Steven Rostedt , Sven Schnelle , Thomas Gleixner , Uladzislau Rezki , Valentin Schneider , Vasily Gorbik , Vincent Guittot , Viresh Kumar , Xin Zhao , linux-pm@vger.kernel.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Shrikanth Hegde Subject: [PATCH 01/15] sched/idle: Handle offlining first in idle loop Date: Fri, 6 Feb 2026 15:22:31 +0100 Message-ID: <20260206142245.58987-2-frederic@kernel.org> X-Mailer: git-send-email 2.51.1 In-Reply-To: <20260206142245.58987-1-frederic@kernel.org> References: <20260206142245.58987-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Offline handling happens from within the inner idle loop, after the beginning of dyntick cputime accounting, nohz idle load balancing and TIF_NEED_RESCHED polling. This is not necessary and even buggy because: * There is no dyntick handling to do. And calling tick_nohz_idle_enter() messes up with the struct tick_sched reset that was performed on tick_sched_timer_dying(). * There is no nohz idle balancing to do. * Polling on TIF_RESCHED is irrelevant at this stage, there are no more tasks allowed to run. * No need to check if need_resched() before offline handling since stop_machine is done and all per-cpu kthread should be done with their job. Therefore move the offline handling at the beginning of the idle loop. This will also ease the idle cputime unification later by not elapsing idle time while offline through the call to: tick_nohz_idle_enter() -> tick_nohz_start_idle() Signed-off-by: Frederic Weisbecker --- kernel/sched/idle.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index c174afe1dd17..51764cbec6f3 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -260,6 +260,14 @@ static void do_idle(void) { int cpu =3D smp_processor_id(); =20 + if (cpu_is_offline(cpu)) { + local_irq_disable(); + /* All per-CPU kernel threads should be done by now. */ + WARN_ON_ONCE(need_resched()); + cpuhp_report_idle_dead(); + arch_cpu_idle_dead(); + } + /* * Check if we need to update blocked load */ @@ -311,11 +319,6 @@ static void do_idle(void) */ local_irq_disable(); =20 - if (cpu_is_offline(cpu)) { - cpuhp_report_idle_dead(); - arch_cpu_idle_dead(); - } - arch_cpu_idle_enter(); rcu_nocb_flush_deferred_wakeup(); =20 --=20 2.51.1