Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755431Ab3GYJIM (ORCPT ); Thu, 25 Jul 2013 05:08:12 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:42193 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753142Ab3GYJFh (ORCPT ); Thu, 25 Jul 2013 05:05:37 -0400 Subject: [RFC PATCH 4/5] cpuidle/ppc: CPU goes tickless if there are no arch-specific constraints To: benh@kernel.crashing.org, paul.gortmaker@windriver.com, paulus@samba.org, shangw@linux.vnet.ibm.com, galak@kernel.crashing.org, fweisbec@gmail.com, paulmck@linux.vnet.ibm.com, michael@ellerman.id.au, arnd@arndb.de, linux-pm@vger.kernel.org, rostedt@goodmis.org, rjw@sisk.pl, john.stultz@linaro.org, tglx@linutronix.de, chenhui.zhao@freescale.com, deepthi@linux.vnet.ibm.com, geoff@infradead.org, linux-kernel@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com, schwidefsky@de.ibm.com, svaidy@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org From: Preeti U Murthy Date: Thu, 25 Jul 2013 14:33:02 +0530 Message-ID: <20130725090302.12500.42998.stgit@preeti.in.ibm.com> In-Reply-To: <20130725090016.12500.28888.stgit@preeti.in.ibm.com> References: <20130725090016.12500.28888.stgit@preeti.in.ibm.com> User-Agent: StGit/0.16-38-g167d MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13072508-3864-0000-0000-000009402A1D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2504 Lines: 67 In the current design of timer offload framework, the broadcast cpu should *not* go into tickless idle so as to avoid missed wakeups on CPUs in deep idle states. Since we prevent the CPUs entering deep idle states from programming the lapic of the broadcast cpu for their respective next local events for reasons mentioned in PATCH[3/5], the broadcast CPU checks if there are any CPUs to be woken up during each of its timer interrupt programmed to its local events. With tickless idle, the broadcast CPU might not get a timer interrupt till after many ticks which can result in missed wakeups on CPUs in deep idle states. By disabling tickless idle, worst case, the tick_sched hrtimer will trigger a timer interrupt every period to check for broadcast. However the current setup of tickless idle does not let us make the choice of tickless on individual cpus. NOHZ_MODE_INACTIVE which disables tickless idle, is a system wide setting. Hence resort to an arch specific call to check if a cpu can go into tickless idle. Signed-off-by: Preeti U Murthy --- arch/powerpc/kernel/time.c | 5 +++++ kernel/time/tick-sched.c | 7 +++++++ 2 files changed, 12 insertions(+) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 8ed0fb3..68a636f 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -862,6 +862,11 @@ static void decrementer_timer_broadcast(const struct cpumask *mask) arch_send_tick_broadcast(mask); } +int arch_can_stop_idle_tick(int cpu) +{ + return cpu != bc_cpu; +} + static void register_decrementer_clockevent(int cpu) { struct clock_event_device *dec = &per_cpu(decrementers, cpu); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 6960172..e9ffa84 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -700,8 +700,15 @@ static void tick_nohz_full_stop_tick(struct tick_sched *ts) #endif } +int __weak arch_can_stop_idle_tick(int cpu) +{ + return 1; +} + static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) { + if (!arch_can_stop_idle_tick(cpu)) + return false; /* * If this cpu is offline and it is the one which updates * jiffies, then give up the assignment and let it be taken by -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/