PM / OPP: RCU reclaim

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.guittot@linaro.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
index d946864..1211210 100644 (file)
--- a/drivers/base/power/opp.c
+++ b/drivers/base/power/opp.c
@@ -65,6 +65,7 @@ struct opp {
        unsigned long u_volt;
 
        struct device_opp *dev_opp;
+       struct rcu_head head;
 };
 
 /**
@@ -442,6 +443,17 @@ 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
@@ -512,7 +524,7 @@ 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)
@@ -522,13 +534,10 @@ 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;
 }