Messages in this thread | | | Date | Wed, 20 Aug 2008 12:14:37 -0700 | From | mark gross <> | Subject | Re: [PATCH RFC] pm_qos_requirement might sleep |
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On Fri, Aug 15, 2008 at 12:51:11AM +0200, John Kacur wrote: > On Thu, Aug 14, 2008 at 7:48 PM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, 2008-08-14 at 08:52 -0700, mark gross wrote: > > > >> Keeping a lock around the different "target_value"s may not be so > >> important. Its just a 32bit scaler value, and perhaps we can make it an > >> atomic type? That way we loose the raw_spinlock. > > > > My suggestion was to keep the locking for the write side - so as to > > avoid stuff stomping on one another, but drop the read side as: > > > > spin_lock > > foo = var; > > spin_unlock > > return foo; > > > > is kinda useless, it doesn't actually serialize against the usage of > > foo, that is, once it gets used, var might already have acquired a new > > value. > > > > The only thing it would protect is reading var, but since that is a > > machine sized read, its atomic anyway (assuming its naturally aligned). > > > > So no need for atomic_t (its read-side is just a read too), just drop > > the whole lock usage from pq_qos_requirement(). > > > > Thanks Peter. > > Mark, is the following patch ok with you? This should be applied to > mainline, and then after that no special patches are necessary for > real-time.
It looks ok to me, do I need to add a compiler declaration to the structure to make sure the target_value is word aligned?
thanks,
--mgross
> > Thanks > > John Kacur
> Subject: Remove unnecessary lock in pm_qos_requirement > > Signed-off-by: John Kacur <jkacur at gmail dot com> > > Index: linux-2.6/kernel/pm_qos_params.c > =================================================================== > --- linux-2.6.orig/kernel/pm_qos_params.c > +++ linux-2.6/kernel/pm_qos_params.c > @@ -193,14 +193,7 @@ static int find_pm_qos_object_by_minor(i > */ > int pm_qos_requirement(int pm_qos_class) > { > - int ret_val; > - unsigned long flags; > - > - spin_lock_irqsave(&pm_qos_lock, flags); > - ret_val = pm_qos_array[pm_qos_class]->target_value; > - spin_unlock_irqrestore(&pm_qos_lock, flags); > - > - return ret_val; > + return pm_qos_array[pm_qos_class]->target_value; > } > EXPORT_SYMBOL_GPL(pm_qos_requirement); >
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