On Wed, 09 Jun 2010 08:38:39 -0400
James Bottomley <James.Bottomley@xxxxxxx> wrote:
> On Wed, 2010-06-09 at 11:46 +0200, Thomas Gleixner wrote:
> > On Wed, 9 Jun 2010, florian@xxxxxxxxxxx wrote:
> >
> > > The pm_qos framework has to guarantee atomic notifications so that
> > > drivers can request and release constraints at all times while no races
> > > occur.
> > >
> > > In order to avoid implementing a secondary notification chain in which
> > > listeners might sleep, we demand that every listener implements it's
> > > notification so that it can run in interrupt context. The listener is in
> > > a better position to know if races are harmful or not.
> >
> > That breaks existing notifiers.
>
> Right ... and we don't want to do that. Which is why I think we just
> use blocking notifiers as they are but allow for creating atomic ones
> which may use atomic update sites.
>
> This is the solution I have in my tree ... it preserves existing
> semantics because all the update and add sites are in user context, but
> it allows for notifiers with purely atomic semantics and will do a
> runtime warn if anyone tries to use them in a blocking fashion (or if
> anyone adds an atomic update to an existing blocking notifier).
>
> James
>
> @@ -302,8 +330,12 @@ int pm_qos_add_notifier(int pm_qos_class, struct notifier_block *notifier)
> {
> int retval;
>
> + /* someone tried to register a blocking notifier to a
> + * qos object that only supports atomic ones */
> + BUG_ON(!pm_qos_array[pm_qos_class]->blocking_notifiers);
> +
> retval = blocking_notifier_chain_register(
> - pm_qos_array[pm_qos_class]->notifiers, notifier);
> + pm_qos_array[pm_qos_class]->blocking_notifiers, notifier);
>
> return retval;
> }
Why not:
retval = 1;
if(pm_qos_array[pm_qos_class]->blocking_notifiers)
retval = blocking_notifier_chain_register(..
else
WARN();
return retval;
That way, the offending programmer could eventually fix it, without
having to reboot?
> @@ -319,15 +351,41 @@ EXPORT_SYMBOL_GPL(pm_qos_add_notifier);
The rest looks good to me. I posted another variant using
schedule_work().
As currently no atomic notifications are needed and critical operations
probably have to check pm_qos_get_request manually anyway to be shure
this would be an alternative. Whatever.
Cheers,
Flo
_______________________________________________
linux-pm mailing list
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/linux-pm
