Re: [linux-pm] [PATCH 02/11] PM: extend PM QoS with per-device wake-up constraints

[Mark Brown <broonie@opensource.wolfsonmicro.com>]

On Fri, Aug 19, 2011 at 10:24:19PM -0400, Alan Stern wrote:
> On Sat, 20 Aug 2011, Mark Brown wrote:

> > interfaces and let the subsystem and driver translate these into actual
> > wakeup latency constraints:

> >   https://lists.linux-foundation.org/pipermail/linux-pm/2011-August/032422.html
> >   https://lists.linux-foundation.org/pipermail/linux-pm/2011-August/032428.html

> > This is much easier for users as it translates into something they're
> > actually doing (and in most cases the driver can make it Just Work) and
> > it means that off the shelf applications will end up tuning the system
> > appropriately by themselves.  I'm additionally concerned that if we
> > expose this stuff directly to userspace that's an open invitation to
> > driver authors to not even bother trying to make the kernel figure this
> > stuff out by itself and to instead tie the system together with magic
> > userspace.

> Can you give a couple of examples to illustrate these points?  I think
> it would help a lot to make the conversation more concrete.

Examples of what?  Latency constraints from drivers?  That'd be things
like Kevin listed in the second message linked above - the kernel knows
it needs to wake up within a given time period in order to have time to
do what it needs to do in response to a given wake source such as
filling a buffer before it underflows.