Re: [PATCH 0/3] Hook up powerclamp with PM QOS and cpuidle

[jacob pan <jacob.jun.pan@linux.intel.com>]

On Wed, 27 Nov 2013 12:56:34 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, Nov 26, 2013 at 03:20:08PM -0800, Jacob Pan wrote:
> > This patchset is intended to address the behavior change and
> > efficiency loss introduced by using consolidated idle routine in
> > powerclamp driver.
> > 
> > Specifically,
> > [PATCH 3/8] idle, thermal, acpi: Remove home grown idle
> > implementations
> > 
> > The motivation is that after using common idle routine, powerclamp
> > driver can no longer pick the deepest idle state needed to conserve
> > power. Idle state is selected by governors which can be influenced
> > by PM QOS and other factors. This patchset hooks up powerclamp idle
> > injection with PM QOS and eventually influce idle governors to pick
> > the power saving target states.
> > 
> > There are some downside of this approach. Due to overhead,
> > communication with PM QOS is at enable/disable idle injection time
> > instead of each injection period. The implication is that if the
> > system natual idle is more than target injected idle, powerclamp
> > will skip some injection period. During this period however,
> > deepest idle state may still be chosen necessarily regardless the
> > latency constraint.
> 
> Does the QoS stuff have a means of notifying its users of constraints
> violation? I suspect some applications might light to be told if their
> requests aren't honoured.
> 
Each class has a notifier. This patchset is calling the notifier
when the qos class is disable/enable. the receiver of these
notifications are in the kernel.

I don't see the qos core code has a way to signal userspace about
target change.