From patchwork Thu Feb 6 17:43:26 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Preeti U Murthy X-Patchwork-Id: 317513 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from ozlabs.org (localhost [IPv6:::1]) by ozlabs.org (Postfix) with ESMTP id 1EE942C03BD for ; Fri, 7 Feb 2014 04:47:41 +1100 (EST) Received: from e28smtp06.in.ibm.com (e28smtp06.in.ibm.com [122.248.162.6]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 2024A2C00B0 for ; Fri, 7 Feb 2014 04:47:05 +1100 (EST) Received: from /spool/local by e28smtp06.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Thu, 6 Feb 2014 23:17:00 +0530 Received: from d28relay05.in.ibm.com (d28relay05.in.ibm.com [9.184.220.62]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id CD3233940062 for ; Thu, 6 Feb 2014 23:16:58 +0530 (IST) Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s16Hl0JL9372038 for ; Thu, 6 Feb 2014 23:17:00 +0530 Received: from d28av03.in.ibm.com (localhost [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s16Hkva3013904 for ; Thu, 6 Feb 2014 23:16:58 +0530 Received: from [9.79.185.231] ([9.79.185.231]) by d28av03.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id s16HktWD013810; Thu, 6 Feb 2014 23:16:56 +0530 Message-ID: <52F3C9BE.4050203@linux.vnet.ibm.com> Date: Thu, 06 Feb 2014 23:13:26 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Thomas Gleixner Subject: Re: [PATCH V3 2/3] tick/cpuidle: Initialize hrtimer mode of broadcast References: <20140206054158.4595.17827.stgit@preeti> <20140206055012.4595.55692.stgit@preeti> In-Reply-To: X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14020617-9574-0000-0000-00000BD27F26 Cc: deepthi@linux.vnet.ibm.com, rafael.j.wysocki@intel.com, linux-pm@vger.kernel.org, peterz@infradead.org, fweisbec@gmail.com, daniel.lezcano@linaro.org, linux-kernel@vger.kernel.org, paulus@samba.org, srivatsa.bhat@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.16 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Thomas, On 02/06/2014 09:33 PM, Thomas Gleixner wrote: > On Thu, 6 Feb 2014, Preeti U Murthy wrote: > > Compiler warnings are not so important, right? > > kernel/time/tick-broadcast.c: In function ‘tick_broadcast_oneshot_control’: > kernel/time/tick-broadcast.c:700:3: warning: ‘return’ with no value, in function returning non-void [-Wreturn-type] > kernel/time/tick-broadcast.c:711:3: warning: ‘return’ with no value, in function returning non-void [-Wreturn-type] My apologies for this, will make sure this will not repeat. On compilation I did not receive any warnings with the additional compile time flags too.I compiled it on powerpc. Let me look into why the warnings did not show up. Nevertheless I should have taken care of this even by simply looking at the code. > >> + /* >> + * If the current CPU owns the hrtimer broadcast >> + * mechanism, it cannot go deep idle. >> + */ >> + ret = broadcast_needs_cpu(bc, cpu); > > So we leave the CPU in the broadcast mask, just to force another call > to the notify code right away to remove it again. Wouldn't it be more > clever to clear the flag right away? That would make the changes to > the cpuidle code simpler. Delta patch below. You are right. > > Thanks, > > tglx > --- > > --- tip.orig/kernel/time/tick-broadcast.c > +++ tip/kernel/time/tick-broadcast.c > @@ -697,7 +697,7 @@ int tick_broadcast_oneshot_control(unsig > * states > */ > if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) > - return; > + return 0; > > /* > * We are called with preemtion disabled from the depth of the > @@ -708,7 +708,7 @@ int tick_broadcast_oneshot_control(unsig > dev = td->evtdev; > > if (!(dev->features & CLOCK_EVT_FEAT_C3STOP)) > - return; > + return 0; > > bc = tick_broadcast_device.evtdev; > > @@ -731,9 +731,14 @@ int tick_broadcast_oneshot_control(unsig > } > /* > * If the current CPU owns the hrtimer broadcast > - * mechanism, it cannot go deep idle. > + * mechanism, it cannot go deep idle and we remove the > + * CPU from the broadcast mask. We don't have to go > + * through the EXIT path as the local timer is not > + * shutdown. > */ > ret = broadcast_needs_cpu(bc, cpu); > + if (ret) > + cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask); > } else { > if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) { > clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT); > > The cpuidle patch then is below. The trace_cpu_idle_rcuidle() functions have been moved around so that the broadcast CPU does not trace any idle event and that the symmetry between the trace functions and the call to the broadcast framework is maintained. Wow, it does become very simple :) time/cpuidle:Handle failed call to BROADCAST_ENTER on archs with CPUIDLE_FLAG_TIMER_STOP set From: Preeti U Murthy Some archs set the CPUIDLE_FLAG_TIMER_STOP flag for idle states in which the local timers stop. The cpuidle_idle_call() currently handles such idle states by calling into the broadcast framework so as to wakeup CPUs at their next wakeup event. With the hrtimer mode of broadcast, the BROADCAST_ENTER call into the broadcast frameowork can fail for archs that do not have an external clock device to handle wakeups and the CPU in question has to thus be made the stand by CPU. This patch handles such cases by failing the call into cpuidle so that the arch can take some default action. The arch will certainly not enter a similar idle state because a failed cpuidle call will also implicitly indicate that the broadcast framework has not registered this CPU to be woken up. Hence we are safe if we fail the cpuidle call. In the process move the functions that trace idle statistics just before and after the entry and exit into idle states respectively. In other scenarios where the call to cpuidle fails, we end up not tracing idle entry and exit since a decision on an idle state could not be taken. Similarly when the call to broadcast framework fails, we skip tracing idle statistics because we are in no further position to take a decision on an alternative idle state to enter into. Signed-off-by: Preeti U Murthy --- drivers/cpuidle/cpuidle.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) Thank you Regards Preeti U Murthy diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a55e68f..8beb0f02 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -140,12 +140,14 @@ int cpuidle_idle_call(void) return 0; } - trace_cpu_idle_rcuidle(next_state, dev->cpu); - broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP); - if (broadcast) - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu); + if (broadcast && + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu)) + return -EBUSY; + + + trace_cpu_idle_rcuidle(next_state, dev->cpu); if (cpuidle_state_is_coupled(dev, drv, next_state)) entered_state = cpuidle_enter_state_coupled(dev, drv, @@ -153,11 +155,11 @@ int cpuidle_idle_call(void) else entered_state = cpuidle_enter_state(dev, drv, next_state); + trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); + if (broadcast) clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu); - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); - /* give the governor an opportunity to reflect on the outcome */ if (cpuidle_curr_governor->reflect) cpuidle_curr_governor->reflect(dev, entered_state);