Messages in this thread | | | Date | Thu, 21 Jul 2011 18:36:43 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 1/3] perf: add context field to perf_event |
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On 07/21/2011 06:32 PM, Will Deacon wrote: > > > > Using TIF_bits sounds like a much better solution for this, wakeups are > > really rather expensive and its best to avoid extra if at all possible. > > The problem with using a TIF bit to tell a task that it needs to perform > some preempt_notifier registrations is that you end up with something that > looks a lot like preempt notifiers! You also don't escape the concurrent > read/write to thelist of pending registrations. > > One thing I tried was simply using an RCU protected hlist for the preempt > notifiers so that we don't have to worry about atomicity when reading the > notifiers in finish_task_switch. It's a bit odd, since we know we only ever > have a single reader, but I've included it below anyway. > > If anybody has any better ideas, I'm all ears.
> +void preempt_notifier_register_task(struct preempt_notifier *notifier, > + struct task_struct *tsk) > +{ > + mutex_lock(&tsk->preempt_notifiers_mutex); > + hlist_add_head_rcu(¬ifier->link,&tsk->preempt_notifiers); > + mutex_unlock(&tsk->preempt_notifiers_mutex); > +} > +EXPORT_SYMBOL_GPL(preempt_notifier_register_task); > + > +void preempt_notifier_unregister_task(struct preempt_notifier *notifier, > + struct task_struct *tsk) > +{ > + mutex_lock(&tsk->preempt_notifiers_mutex); > + hlist_del_rcu(¬ifier->link); > + mutex_unlock(&tsk->preempt_notifiers_mutex); > +} > +EXPORT_SYMBOL_GPL(preempt_notifier_unregister_task); > + > /** > * preempt_notifier_register - tell me when current is being preempted& rescheduled > * @notifier: notifier struct to register > */ > void preempt_notifier_register(struct preempt_notifier *notifier) > { > - hlist_add_head(¬ifier->link,¤t->preempt_notifiers); > + preempt_notifier_register_task(notifier, current); > } > EXPORT_SYMBOL_GPL(preempt_notifier_register);
This is (and must be) called from a preempt disabled context, no mutexes around here.
-- error compiling committee.c: too many arguments to function
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