Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750991AbaKYRkv (ORCPT ); Tue, 25 Nov 2014 12:40:51 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:39150 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750791AbaKYRku (ORCPT ); Tue, 25 Nov 2014 12:40:50 -0500 Message-ID: <5474BF19.3040707@arm.com> Date: Tue, 25 Nov 2014 17:40:41 +0000 From: Marc Zyngier User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.2.0 MIME-Version: 1.0 To: Daniel Thompson , Thomas Gleixner , Jason Cooper CC: Russell King , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "patches@linaro.org" , "linaro-kernel@lists.linaro.org" , John Stultz , Sumit Semwal , Dirk Behme , Daniel Drake , Dmitry Pervushin , Tim Sander Subject: Re: [PATCH 3.18-rc3 v9 1/5] irqchip: gic: Finer grain locking for gic_raise_softirq References: <1415968543-29469-1-git-send-email-daniel.thompson@linaro.org> <1416936401-5147-1-git-send-email-daniel.thompson@linaro.org> <1416936401-5147-2-git-send-email-daniel.thompson@linaro.org> In-Reply-To: <1416936401-5147-2-git-send-email-daniel.thompson@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Daniel, On 25/11/14 17:26, Daniel Thompson wrote: > irq_controller_lock is used for multiple purposes within the gic driver. > Primarily it is used to make register read-modify-write sequences atomic. > It is also used by gic_raise_softirq() in order that the big.LITTLE > migration logic can figure out when it is safe to migrate interrupts > between physical cores. > > The second usage of irq_controller_lock is difficult to discern when > reviewing the code because the migration itself takes place outside > the lock. > > This patch makes the second usage more explicit by splitting it out into > a separate lock and providing better comments. While we're at it, how about an additional patch that would make this lock disappear entirely when the big-little stuff is not compiled in, which is likely to be the case on a lot of (dare I say most?) systems? That will save expensive barriers that we definitely could do without. It otherwise looks good to me. Thanks, M. > Signed-off-by: Daniel Thompson > Cc: Thomas Gleixner > Cc: Jason Cooper > Cc: Russell King > Cc: Marc Zyngier > --- > drivers/irqchip/irq-gic.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c > index 38493ff28fa5..bb4bc20573ea 100644 > --- a/drivers/irqchip/irq-gic.c > +++ b/drivers/irqchip/irq-gic.c > @@ -73,6 +73,12 @@ struct gic_chip_data { > static DEFINE_RAW_SPINLOCK(irq_controller_lock); > > /* > + * This lock is used by the big.LITTLE migration code to ensure no > + * IPIs can be pended on the old core after the map has been updated. > + */ > +static DEFINE_RAW_SPINLOCK(cpu_map_migration_lock); > + > +/* > * The GIC mapping of CPU interfaces does not necessarily match > * the logical CPU numbering. Let's use a mapping as returned > * by the GIC itself. > @@ -624,7 +630,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) > int cpu; > unsigned long flags, map = 0; > > - raw_spin_lock_irqsave(&irq_controller_lock, flags); > + raw_spin_lock_irqsave(&cpu_map_migration_lock, flags); > > /* Convert our logical CPU mask into a physical one. */ > for_each_cpu(cpu, mask) > @@ -639,7 +645,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) > /* this always happens on GIC0 */ > writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT); > > - raw_spin_unlock_irqrestore(&irq_controller_lock, flags); > + raw_spin_unlock_irqrestore(&cpu_map_migration_lock, flags); > } > #endif > > @@ -710,8 +716,17 @@ void gic_migrate_target(unsigned int new_cpu_id) > > raw_spin_lock(&irq_controller_lock); > > - /* Update the target interface for this logical CPU */ > + /* > + * Update the target interface for this logical CPU > + * > + * From the point we release the cpu_map_migration_lock any new > + * SGIs will be pended on the new cpu which makes the set of SGIs > + * pending on the old cpu static. That means we can defer the > + * migration until after we have released the irq_controller_lock. > + */ > + raw_spin_lock(&cpu_map_migration_lock); > gic_cpu_map[cpu] = 1 << new_cpu_id; > + raw_spin_unlock(&cpu_map_migration_lock); > > /* > * Find all the peripheral interrupts targetting the current > -- Jazz is not dead. It just smells funny... -- 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/