Re: [RFC PATCH 1/2] mac80211: make max_network_latency notifier atomic safe

[Florian Mickler <florian@mickler.org>]

On Wed, 09 Jun 2010 11:38:07 +0200
Johannes Berg <johannes@sipsolutions.net> wrote:

> On Wed, 2010-06-09 at 11:15 +0200, florian@mickler.org wrote:
> > In order to have the pm_qos framework be callable from interrupt
> > context, all listeners have to also be callable in that context.
> 
> That makes no sense at all. Why add work structs _everywhere_ in the
> callees and make the API harder to use and easy to get wrong completely,
> instead of just adding a single work struct that will be queued from the
> caller and dealing with the locking complexity etc. just once.
> 
> johannes

Just to defend this approach, but I'm certainly not married to it
(hence RFC):

There are only two listeners at the moment. I suspect that most future
uses of the framework need to be atomic, as the driver that
requests a specific quality of service probably doesn't want to get into
races with the provider of that service(listener). So i suspected the
network listener to be the special case.  

The race between service-provider and qos-requester for non-atomic
contextes is already there, isn't it? so, locking complexity shouldn't
be worse than before.

But my first approach to this is seen here:
https://lists.linux-foundation.org/pipermail/linux-pm/2010-June/026902.html

A third possibility would be to make it dependent on the
type of the constraint, if blocking notifiers are allowed or not. 
But that would sacrifice API consistency (update_request for one
constraint is allowed to be called in interrupt context and
update_request for another would be not).

Cheers,
Flo