From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [PATCH v4] pm_qos: make update_request non blocking Date: Wed, 09 Jun 2010 11:37:12 -0400 Message-ID: <1276097832.4343.223.camel__37639.1528793194$1276097972$gmane$org@mulgrave.site> References: <1276097381-3982-1-git-send-email-florian@mickler.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1276097381-3982-1-git-send-email-florian@mickler.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: florian@mickler.org Cc: Jonathan Corbet , Frederic Weisbecker , markgross@thegnar.org, linville@tuxdriver.com, linux-kernel@vger.kernel.org, pm list , Thomas Gleixner List-Id: linux-pm@vger.kernel.org On Wed, 2010-06-09 at 17:29 +0200, florian@mickler.org wrote: > In order to allow drivers to use pm_qos_update_request from interrupt > context we call the notifiers via schedule_work(). > > Signed-off-by: Florian Mickler > --- > > Well, this would be the schedule_work() alternative. > > kernel/pm_qos_params.c | 47 ++++++++++++++++++++++++++++++----------------- > 1 files changed, 30 insertions(+), 17 deletions(-) > > diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c > index f42d3f7..296343a 100644 > --- a/kernel/pm_qos_params.c > +++ b/kernel/pm_qos_params.c > @@ -40,6 +40,7 @@ > #include > #include > #include > +#include > > #include > > @@ -60,11 +61,13 @@ struct pm_qos_request_list { > > static s32 max_compare(s32 v1, s32 v2); > static s32 min_compare(s32 v1, s32 v2); > +static void update_notify(struct work_struct *work); > > struct pm_qos_object { > struct pm_qos_request_list requests; > struct blocking_notifier_head *notifiers; > struct miscdevice pm_qos_power_miscdev; > + struct work_struct notify; > char *name; > s32 default_value; > atomic_t target_value; > @@ -72,10 +75,12 @@ struct pm_qos_object { > }; > > static struct pm_qos_object null_pm_qos; > + > static BLOCKING_NOTIFIER_HEAD(cpu_dma_lat_notifier); > static struct pm_qos_object cpu_dma_pm_qos = { > .requests = {LIST_HEAD_INIT(cpu_dma_pm_qos.requests.list)}, > .notifiers = &cpu_dma_lat_notifier, > + .notify = __WORK_INITIALIZER(cpu_dma_pm_qos.notify, update_notify), > .name = "cpu_dma_latency", > .default_value = 2000 * USEC_PER_SEC, > .target_value = ATOMIC_INIT(2000 * USEC_PER_SEC), > @@ -86,6 +91,7 @@ static BLOCKING_NOTIFIER_HEAD(network_lat_notifier); > static struct pm_qos_object network_lat_pm_qos = { > .requests = {LIST_HEAD_INIT(network_lat_pm_qos.requests.list)}, > .notifiers = &network_lat_notifier, > + .notify = __WORK_INITIALIZER(network_lat_pm_qos.notify, update_notify), > .name = "network_latency", > .default_value = 2000 * USEC_PER_SEC, > .target_value = ATOMIC_INIT(2000 * USEC_PER_SEC), > @@ -97,13 +103,14 @@ static BLOCKING_NOTIFIER_HEAD(network_throughput_notifier); > static struct pm_qos_object network_throughput_pm_qos = { > .requests = {LIST_HEAD_INIT(network_throughput_pm_qos.requests.list)}, > .notifiers = &network_throughput_notifier, > + .notify = __WORK_INITIALIZER(network_throughput_pm_qos.notify, > + update_notify), > .name = "network_throughput", > .default_value = 0, > .target_value = ATOMIC_INIT(0), > .comparitor = max_compare > }; > > - > static struct pm_qos_object *pm_qos_array[] = { > &null_pm_qos, > &cpu_dma_pm_qos, > @@ -135,35 +142,40 @@ static s32 min_compare(s32 v1, s32 v2) > return min(v1, v2); > } > > +static void update_notify(struct work_struct *work) > +{ > + struct pm_qos_object *obj = > + container_of(work, struct pm_qos_object, notify); > + > + s32 extreme_value = atomic_read(&obj->target_value); > + blocking_notifier_call_chain( > + obj->notifiers, > + (unsigned long) extreme_value, NULL); > +} > > static void update_target(int pm_qos_class) > { > s32 extreme_value; > struct pm_qos_request_list *node; > + struct pm_qos_object *obj = pm_qos_array[pm_qos_class]; > unsigned long flags; > int call_notifier = 0; > > spin_lock_irqsave(&pm_qos_lock, flags); > - extreme_value = pm_qos_array[pm_qos_class]->default_value; > - list_for_each_entry(node, > - &pm_qos_array[pm_qos_class]->requests.list, list) { > - extreme_value = pm_qos_array[pm_qos_class]->comparitor( > - extreme_value, node->value); > - } > - if (atomic_read(&pm_qos_array[pm_qos_class]->target_value) != > - extreme_value) { > + extreme_value = obj->default_value; > + list_for_each_entry(node, &obj->requests.list, list) > + extreme_value = obj->comparitor(extreme_value, node->value); > + > + if (atomic_read(&obj->target_value) != extreme_value) { > call_notifier = 1; > - atomic_set(&pm_qos_array[pm_qos_class]->target_value, > - extreme_value); > + atomic_set(&obj->target_value, extreme_value); > pr_debug(KERN_ERR "new target for qos %d is %d\n", pm_qos_class, > - atomic_read(&pm_qos_array[pm_qos_class]->target_value)); > + atomic_read(&obj->target_value)); > } > spin_unlock_irqrestore(&pm_qos_lock, flags); > > if (call_notifier) > - blocking_notifier_call_chain( > - pm_qos_array[pm_qos_class]->notifiers, > - (unsigned long) extreme_value, NULL); > + schedule_work(&obj->notify); > } This still isn't resilient against two successive calls to update. If the second one gets to schedule_work() before the work of the first one has finished, you'll corrupt the workqueue. The mechanisms to solve this race (refcounting a pool of structures) are so heavyweight that I concluded it was simpler just to have atomically updated pm_qos objects and enforce it ... rather than trying to allow blocking chains to be added to atomic sites via a workqueue. James