On Tue, Oct 02, 2012 at 04:02:05AM +0200, Rafael J. Wysocki wrote:
> On Monday 01 of October 2012 15:42:39 Vincent Guittot wrote:
> > Hi Rafael,
> >
> > Ping.
>
> I'm considering this for v3.8, but I'd like Paul (CCed) to tell me what he
> thinks about it.
Looks good to me -- the only thing deferred is the freeing of memory.
The only risk is that fast repeated invocation of opp_set_availability()
could result in a lot of memory waiting for RCU grace periods, but
call_rcu() has code to prevent this. So:
Reviewed-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Thanks,
> Rafael
>
>
> > On 25 September 2012 15:42, Vincent Guittot <vincent.guit...@linaro.org>
> > wrote:
> > > synchronize_rcu blocks the caller of opp_enable/disbale
> > > for a complete grace period. This blocking duration prevents
> > > any intensive use of the functions. Replace synchronize_rcu
> > > by call_rcu which will call our function for freeing the old
> > > opp element.
> > >
> > > The duration of opp_enable and opp_disable will be no more
> > > dependant of the grace period.
> > >
> > > Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> > > ---
> > > drivers/base/power/opp.c | 19 ++++++++++++++-----
> > > 1 file changed, 14 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> > > index ac993ea..49e4626 100644
> > > --- a/drivers/base/power/opp.c
> > > +++ b/drivers/base/power/opp.c
> > > @@ -64,6 +64,7 @@ struct opp {
> > > unsigned long u_volt;
> > >
> > > struct device_opp *dev_opp;
> > > + struct rcu_head head;
> > > };
> > >
> > > /**
> > > @@ -441,6 +442,17 @@ int opp_add(struct device *dev, unsigned long freq,
> > > unsigned long u_volt)
> > > }
> > >
> > > /**
> > > + * opp_free_rcu() - helper to clear the struct opp when grace period has
> > > + * elapsed without blocking the the caller of opp_set_availability
> > > + */
> > > +static void opp_free_rcu(struct rcu_head *head)
> > > +{
> > > + struct opp *opp = container_of(head, struct opp, head);
> > > +
> > > + kfree(opp);
> > > +}
> > > +
> > > +/**
> > > * opp_set_availability() - helper to set the availability of an opp
> > > * @dev: device for which we do this operation
> > > * @freq: OPP frequency to modify availability
> > > @@ -511,7 +523,7 @@ static int opp_set_availability(struct device *dev,
> > > unsigned long freq,
> > >
> > > list_replace_rcu(&opp->node, &new_opp->node);
> > > mutex_unlock(&dev_opp_list_lock);
> > > - synchronize_rcu();
> > > + call_rcu(&opp->head, opp_free_rcu);
> > >
> > > /* Notify the change of the OPP availability */
> > > if (availability_req)
> > > @@ -521,13 +533,10 @@ static int opp_set_availability(struct device *dev,
> > > unsigned long freq,
> > > srcu_notifier_call_chain(&dev_opp->head,
> > > OPP_EVENT_DISABLE,
> > > new_opp);
> > >
> > > - /* clean up old opp */
> > > - new_opp = opp;
> > > - goto out;
> > > + return 0;
> > >
> > > unlock:
> > > mutex_unlock(&dev_opp_list_lock);
> > > -out:
> > > kfree(new_opp);
> > > return r;
> > > }
> > > --
> > > 1.7.9.5
> > >
> > --
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> >
>
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