Re: [PATCH] pm_qos: remove unnecessary list-traversal

mark gross
2010-06-01T14:07:59Z

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
>