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    SubjectRe: [PATCH] pm_qos: remove unnecessary list-traversal
    On Tue, Jun 01, 2010 at 10:46:54AM +0200, florian@mickler.org wrote:
    > The new extreme value is only depending on the old extreme value and
    > the changed value.
    >
    > Signed-off-by: Florian Mickler <florian@mickler.org>
    > ---
    > kernel/pm_qos_params.c | 19 +++++++++++++++++--
    > 1 files changed, 17 insertions(+), 2 deletions(-)
    >
    > diff --git a/kernel/pm_qos_params.c b/kernel/pm_qos_params.c
    > index f42d3f7..5d71c12 100644
    > --- a/kernel/pm_qos_params.c
    > +++ b/kernel/pm_qos_params.c
    > @@ -136,6 +136,16 @@ static s32 min_compare(s32 v1, s32 v2)
    > }
    >
    >
    > +static void update_target_val(int pm_qos_class, s32 val)
    > +{
    > + s32 extreme_value;
    > + s32 new_value;
    > + extreme_value = atomic_read(&pm_qos_array[pm_qos_class]->target_value);
    > + new_value = pm_qos_array[pm_qos_class]->comparitor(val,extreme_value);
    > + if (extreme_value != new_value)
    > + atomic_set(&pm_qos_array[pm_qos_class]->target_value,new_value);
    > +}
    > +

    only works right when the new val is a more stringent constraint
    (request) than what is already there. When removing or reducing a
    constraint (request) the list still needs to be walked to get the new
    aggregate request.

    But its a really good optimization for 1/2 of the calls to pm_qos I
    should have seen and included a long time ago! Thanks!

    --mgross


    > static void update_target(int pm_qos_class)
    > {
    > s32 extreme_value;
    > @@ -253,19 +263,24 @@ void pm_qos_update_request(struct pm_qos_request_list *pm_qos_req,
    > s32 temp;
    >
    > if (pm_qos_req) { /*guard against callers passing in null */
    > + int target = pm_qos_req->pm_qos_class;
    > spin_lock_irqsave(&pm_qos_lock, flags);
    > if (new_value == PM_QOS_DEFAULT_VALUE)
    > - temp = pm_qos_array[pm_qos_req->pm_qos_class]->default_value;
    > + temp = pm_qos_array[target]->default_value;
    > else
    > temp = new_value;
    >
    > if (temp != pm_qos_req->value) {
    > pending_update = 1;
    > pm_qos_req->value = temp;
    > + update_target_val(target,temp);
    > }
    > spin_unlock_irqrestore(&pm_qos_lock, flags);
    > +
    > if (pending_update)
    > - update_target(pm_qos_req->pm_qos_class);
    > + blocking_notifier_call_chain(
    > + pm_qos_array[pm_qos_class]->notifiers,
    > + (unsigned long) temp, NULL);
    > }
    > }
    > EXPORT_SYMBOL_GPL(pm_qos_update_request);
    > --
    > 1.7.1
    >


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