From nobody Sun Feb 8 15:25:50 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 2348613249C; Mon, 26 Feb 2024 22:24:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708986273; cv=none; b=b9RIEG1N0H08R87aB1dMhfIEtAcPLe3PGN3So8FL5YjhHqQsiAVsNBt2Xct25TpWulLKa1o+FI2cbYNoVDbJrtqVPVPdYS+a6YYU3+lUBcehVumh4Lqis6V3aYj5/66AFjcxFcybDF+RKwYlfePbiqWBBEMlCSEDKxLryGjy8D4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708986273; c=relaxed/simple; bh=YK+gb9/jyy0d4w+W35SvBsoEycHJgPqX6bWivLKiY4s=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=AVs2uq581RHbBkUdtJPd6wze+eJSFXnjcQApoNk22wW9Ja0gQ0MU16PcwLiDQFfj0l3FFsNALTFc6ANZCVdF5o7dnX8zNydPGhJzF9ORNtPGRawaL3s+GobvIItN+nKxxxlQYldZgRDPSAbue6eodLGPwfIMUI47SnpK17zQMIA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=xKctK12h; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=WIyTqlVn; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="xKctK12h"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="WIyTqlVn" Date: Mon, 26 Feb 2024 22:24:29 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1708986270; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7xTIw5tqjVZIpH35eKhPSVJAIAlEyQ7W8yT+EkIHaiU=; b=xKctK12hz6sSi2+3JHUeonMCANn+ucQj+nDgM1lZU62YF4VFr+olrcY6ija4vWmqzBK6n7 GsloVN3IpREor1dN/e5f3SMHW+jhO2HAFiIZeTew+/93lu6fCjYbwv9epNiK157TUBIPSS nXn97a5a9G9FHOL4Ancr+2xkzVKbPJBCHw59Jl3JRV1VqcBPg05Qr9exx8C1Y5q6p31nKs oVbClVgPDy14BWOxZE0hA4ztryoWj7+NLZM2IuzZZVi1/TIslfqf/R+JjaIoqs1Jzmb224 xnZ5BUOdRM5CFa6iVCrdP4rTksdWOt2ZverryyU1BqW9fZSdK8Dxaai4BCg9eQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1708986270; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7xTIw5tqjVZIpH35eKhPSVJAIAlEyQ7W8yT+EkIHaiU=; b=WIyTqlVnIs42Jg+6nIgywv2yvw6itLiCb3YvKpw19N714FS0zWLMZVwG49s2Q2RemhVaiC sxZhyoNOIXCArKBA== From: "tip-bot2 for Frederic Weisbecker" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] tick: Shut down low-res tick from dying CPU Cc: Frederic Weisbecker , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240225225508.11587-15-frederic@kernel.org> References: <20240225225508.11587-15-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <170898626934.398.2472263585670806931.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the timers/core branch of tip: Commit-ID: 3f69d04e146c6e14ccdd4e7b37d93f789229202a Gitweb: https://git.kernel.org/tip/3f69d04e146c6e14ccdd4e7b37d93f789= 229202a Author: Frederic Weisbecker AuthorDate: Sun, 25 Feb 2024 23:55:06 +01:00 Committer: Thomas Gleixner CommitterDate: Mon, 26 Feb 2024 11:37:32 +01:00 tick: Shut down low-res tick from dying CPU The timekeeping duty is handed over from the outgoing CPU within stop machine. This works well if CONFIG_NO_HZ_COMMON=3Dn or the tick is in high-res mode. However in low-res dynticks mode, the tick isn't cancelled until the clockevent is shut down, which can happen later. The tick may therefore fire again once IRQs are re-enabled on stop machine and until IRQs are disabled for good upon the last call to idle. That's so many opportunities for a timekeeper to go idle and the outgoing CPU to take over that duty. This is why tick_nohz_idle_stop_tick() is called one last time on idle if the CPU is seen offline: so that the timekeeping duty is handed over again in case the CPU has re-taken the duty. This means there are two timekeeping handovers on CPU down hotplug with different undocumented constraints and purposes: 1) A handover on stop machine for !dynticks || highres. All online CPUs are guaranteed to be non-idle and the timekeeping duty can be safely handed-over. The hrtimer tick is cancelled so it is guaranteed that in dynticks mode the outgoing CPU won't take again the duty. 2) A handover on last idle call for dynticks && lowres. Setting the duty to TICK_DO_TIMER_NONE makes sure that a CPU will take over the timekeeping. Prepare for consolidating the handover to a single place (the first one) with shutting down the low-res tick as well from tick_cancel_sched_timer() as well. This will simplify the handover and unify the tick cancellation between high-res and low-res. Signed-off-by: Frederic Weisbecker Signed-off-by: Thomas Gleixner Reviewed-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240225225508.11587-15-frederic@kernel.org --- kernel/time/tick-common.c | 3 ++- kernel/time/tick-sched.c | 32 +++++++++++++++++++++++++------- kernel/time/tick-sched.h | 4 ++-- 3 files changed, 29 insertions(+), 10 deletions(-) diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 5224140..9cd09ee 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -410,7 +410,8 @@ int tick_cpu_dying(unsigned int dying_cpu) if (tick_do_timer_cpu =3D=3D dying_cpu) tick_do_timer_cpu =3D cpumask_first(cpu_online_mask); =20 - tick_cancel_sched_timer(dying_cpu); + /* Make sure the CPU won't try to retake the timekeeping duty */ + tick_sched_timer_dying(dying_cpu); =20 /* Remove CPU from timer broadcasting */ tick_offline_cpu(dying_cpu); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index dcb9f03..89d16b8 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -308,6 +308,14 @@ static enum hrtimer_restart tick_nohz_handler(struct h= rtimer *timer) return HRTIMER_RESTART; } =20 +static void tick_sched_timer_cancel(struct tick_sched *ts) +{ + if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) + hrtimer_cancel(&ts->sched_timer); + else if (tick_sched_flag_test(ts, TS_FLAG_NOHZ)) + tick_program_event(KTIME_MAX, 1); +} + #ifdef CONFIG_NO_HZ_FULL cpumask_var_t tick_nohz_full_mask; EXPORT_SYMBOL_GPL(tick_nohz_full_mask); @@ -1040,10 +1048,7 @@ static void tick_nohz_stop_tick(struct tick_sched *t= s, int cpu) * the tick timer. */ if (unlikely(expires =3D=3D KTIME_MAX)) { - if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) - hrtimer_cancel(&ts->sched_timer); - else - tick_program_event(KTIME_MAX, 1); + tick_sched_timer_cancel(ts); return; } =20 @@ -1598,14 +1603,27 @@ void tick_setup_sched_timer(bool hrtimer) tick_nohz_activate(ts); } =20 -void tick_cancel_sched_timer(int cpu) +/* + * Shut down the tick and make sure the CPU won't try to retake the timeke= eping + * duty before disabling IRQs in idle for the last time. + */ +void tick_sched_timer_dying(int cpu) { + struct tick_device *td =3D &per_cpu(tick_cpu_device, cpu); struct tick_sched *ts =3D &per_cpu(tick_cpu_sched, cpu); + struct clock_event_device *dev =3D td->evtdev; ktime_t idle_sleeptime, iowait_sleeptime; unsigned long idle_calls, idle_sleeps; =20 - if (tick_sched_flag_test(ts, TS_FLAG_HIGHRES)) - hrtimer_cancel(&ts->sched_timer); + /* This must happen before hrtimers are migrated! */ + tick_sched_timer_cancel(ts); + + /* + * If the clockevents doesn't support CLOCK_EVT_STATE_ONESHOT_STOPPED, + * make sure not to call low-res tick handler. + */ + if (tick_sched_flag_test(ts, TS_FLAG_NOHZ)) + dev->event_handler =3D clockevents_handle_noop; =20 idle_sleeptime =3D ts->idle_sleeptime; iowait_sleeptime =3D ts->iowait_sleeptime; diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h index bbe72a0..58d8d1c 100644 --- a/kernel/time/tick-sched.h +++ b/kernel/time/tick-sched.h @@ -106,9 +106,9 @@ extern struct tick_sched *tick_get_tick_sched(int cpu); =20 extern void tick_setup_sched_timer(bool hrtimer); #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS -extern void tick_cancel_sched_timer(int cpu); +extern void tick_sched_timer_dying(int cpu); #else -static inline void tick_cancel_sched_timer(int cpu) { } +static inline void tick_sched_timer_dying(int cpu) { } #endif =20 #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST