Messages in this thread Patch in this message | | | Date | Wed, 9 Jun 2010 17:27:14 +0200 | From | Florian Mickler <> | Subject | Re: [PATCH 2/2] pm_qos: make update_request callable from interrupt context |
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On Wed, 09 Jun 2010 08:38:39 -0400 James Bottomley <James.Bottomley@suse.de> wrote:
> On Wed, 2010-06-09 at 11:46 +0200, Thomas Gleixner wrote: > > On Wed, 9 Jun 2010, florian@mickler.org 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
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