Re: adding handles to pm_qos?

["Ai Li" <aili@codeaurora.org>]

> How often are you calling pm_qos_update_requirement?
> 
> I think calling pm_qos_ interfaces too often makes me wonder
> about my
> assumptions and your sanity.
> 
> Can you explain why the pm_qos_update_requirement is getting hit
> often
> enough to bother with this change?
> 
> Other than that I don't have a problem with moving to handles,
> if its a
> practical change made for reasons other than making api abuse
> less
> painful.
> 
> Further, If the implicit assumption that pmqos calls are on cold
> paths
> is wrong, then perhaps more thought is needed than just changing
> things
> to handle based searches.
> 

Our embedded platforms support different low power modes.  With the
modes, the deeper the sleep, the more the power savings, and the
larger the interrupt latency coming out of the low power mode.

To help the platform achieving greatest power savings, some of our
device drivers set lateny qos only when there is a service request to
the driver or a device transaction.  When the transaction or request
is done, the drivers cancel the QoS with
pm_qos_update_requirement(PM_QOS_DEFAULT_VALUE), allowing the
platform to reach a deeper sleep.  

The approach gives us good power savings.  However when there are
lots of transactions, pm_qos_update_requirement() gets called a lot
of times.

~Ai