linux-kernel - Re: [PATCH 3/3] pm_qos: only schedule work when in interrupt context

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Date:	Thu, 17 Jun 2010 18:02:25 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Florian Mickler <florian@...kler.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Jonathan Corbet <corbet@....net>, markgross@...gnar.org,
	linville@...driver.com, linux-kernel@...r.kernel.org,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] pm_qos: only schedule work when in interrupt
 context

On Tue, 2010-06-15 at 19:23 +0200, Florian Mickler wrote:
> Hi James!
> 
> On Mon, 14 Jun 2010 16:46:40 +0200
> florian@...kler.org wrote:
> 
> > With this patch we only schedule the work when in interrupt context.
> > 
> > Before update_request was callable from interrupt-context there was a
> > 1:1 relation between a change in the request-value and a notification.
> > This patch restores that behaviour for all constraints that have update_request
> > never called from interrupt context.
> > 
> > The notifier mutex serializes calls to blocking_notifier_call_chain, so
> > that we are serialized against any pending or currently executing notification.
> > 
> > Signed-off-by: Florian Mickler <florian@...kler.org>
> > ---
> >  kernel/pm_qos_params.c |   10 +++++++---
> >  1 files changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
> > index 9346906..c06cae9 100644
> > --- a/kernel/pm_qos_params.c
> > +++ b/kernel/pm_qos_params.c
> > @@ -152,11 +152,15 @@ static s32 min_compare(s32 v1, s32 v2)
> >  static void pm_qos_call_notifiers(struct pm_qos_object *o,
> >  				  unsigned long curr_value)
> >  {
> > -	schedule_work(&o->notify);
> > -
> >  	if (o->atomic_notifiers)
> >  		atomic_notifier_call_chain(o->atomic_notifiers,
> > -					   curr_value, NULL);
> > +				(unsigned long) curr_value, NULL);
> > +
> > +	if (in_interrupt()) 
> > +		schedule_work(&o->notify);
> > +	else 
> > +		blocking_notifier_call_chain(o->blocking_notifiers, 
> > +				(unsigned long) curr_value, NULL);
> >  }
> >  
> >  static void update_notify(struct work_struct *work)
> 
> What about this? Is this ok? I don't know if it is benign to use
> in_interrupt() here. I took this idea from the
> execute_in_process_context() implementation. 

I think it will work ... but I still think it's over complex given the
listed requirements (android seems to only want atomic notifiers from
atomic contexts).

> If this is ok, should I rebase them on your two pm_qos patches (plists
> and the kzalloc removal)? 

Well, I would say yes.  However, for more impartial advice, I'd wait and
see what the pm maintainers want.

> Did you already thought about some debugging stuff that would suffice
> the android needs? I kind of thought about either registerieng some
> notifier callback or using the perf/tracing infrastructure. 
> But I have not looked into it yet.

I was just going to try the conversion when the wakelocks stuff was
finally in and see if it worked in an android kernel.

James


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