From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759237Ab2EIV0g (ORCPT ); Wed, 9 May 2012 17:26:36 -0400 Received: from ogre.sisk.pl ([193.178.161.156]:34505 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751720Ab2EIV0f (ORCPT ); Wed, 9 May 2012 17:26:35 -0400 From: "Rafael J. Wysocki" To: Colin Cross Subject: Re: [PATCHv4 4/4] cpuidle: coupled: add parallel barrier function Date: Wed, 9 May 2012 23:31:24 +0200 User-Agent: KMail/1.13.6 (Linux/3.4.0-rc6+; KDE/4.6.0; x86_64; ; ) Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@lists.linux-foundation.org, Kevin Hilman , Len Brown , Trinabh Gupta , Arjan van de Ven , Deepthi Dharwar , "Greg Kroah-Hartman" , Kay Sievers , Santosh Shilimkar , Daniel Lezcano , Amit Kucheria , Lorenzo Pieralisi , Arnd Bergmann , Russell King References: <1336438662-10484-1-git-send-email-ccross@android.com> <1336438662-10484-5-git-send-email-ccross@android.com> In-Reply-To: <1336438662-10484-5-git-send-email-ccross@android.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-2" Content-Transfer-Encoding: 7bit Message-Id: <201205092331.24487.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday, May 08, 2012, Colin Cross wrote: > Adds cpuidle_coupled_parallel_barrier, which can be used by coupled > cpuidle state enter functions to handle resynchronization after > determining if any cpu needs to abort. The normal use case will > be: > > static bool abort_flag; > static atomic_t abort_barrier; > > int arch_cpuidle_enter(struct cpuidle_device *dev, ...) > { > if (arch_turn_off_irq_controller()) { > /* returns an error if an irq is pending and would be lost > if idle continued and turned off power */ > abort_flag = true; > } > > cpuidle_coupled_parallel_barrier(dev, &abort_barrier); > > if (abort_flag) { > /* One of the cpus didn't turn off it's irq controller */ > arch_turn_on_irq_controller(); > return -EINTR; > } > > /* continue with idle */ > ... > } > > This will cause all cpus to abort idle together if one of them needs > to abort. > > Reviewed-by: Santosh Shilimkar > Tested-by: Santosh Shilimkar > Reviewed-by: Kevin Hilman > Tested-by: Kevin Hilman > Signed-off-by: Colin Cross > --- > drivers/cpuidle/coupled.c | 37 +++++++++++++++++++++++++++++++++++++ > include/linux/cpuidle.h | 4 ++++ > 2 files changed, 41 insertions(+), 0 deletions(-) > > diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c > index 93101fb..3e65de1 100644 > --- a/drivers/cpuidle/coupled.c > +++ b/drivers/cpuidle/coupled.c > @@ -130,6 +130,43 @@ struct cpuidle_coupled { > static cpumask_t cpuidle_coupled_poked_mask; > > /** > + * cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus > + * @dev: cpuidle_device of the calling cpu > + * @a: atomic variable to hold the barrier > + * > + * No caller to this function will return from this function until all online > + * cpus in the same coupled group have called this function. Once any caller > + * has returned from this function, the barrier is immediately available for > + * reuse. > + * > + * The atomic variable a must be initialized to 0 before any cpu calls > + * this function, will be reset to 0 before any cpu returns from this function. > + * > + * Must only be called from within a coupled idle state handler > + * (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set). > + * > + * Provides full smp barrier semantics before and after calling. > + */ > +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a) > +{ > + int n = dev->coupled->online_count; > + > + smp_mb__before_atomic_inc(); > + atomic_inc(a); > + > + while (atomic_read(a) < n) > + cpu_relax(); > + > + if (atomic_inc_return(a) == n * 2) { > + atomic_set(a, 0); > + return; > + } > + > + while (atomic_read(a) > n) > + cpu_relax(); > +} Well, this looks like "wait until all CPUs execute this code". Don't we have anything like this already somewhere? > + > +/** > * cpuidle_state_is_coupled - check if a state is part of a coupled set > * @dev: struct cpuidle_device for the current cpu > * @drv: struct cpuidle_driver for the platform > diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h > index 6038448..5ab7183 100644 > --- a/include/linux/cpuidle.h > +++ b/include/linux/cpuidle.h > @@ -183,6 +183,10 @@ static inline int cpuidle_wrap_enter(struct cpuidle_device *dev, > > #endif > > +#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED > +void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a); > +#endif Why exactly is the extra Kconfig option necessary? > + > /****************************** > * CPUIDLE GOVERNOR INTERFACE * > ******************************/ Rafael