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Date: Wed, 27 Nov 2013 12:56:34 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Linux PM <linux-pm@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Len Brown <len.brown@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Zhang Rui <rui.zhang@intel.com>
Subject: Re: [PATCH 0/3] Hook up powerclamp with PM QOS and cpuidle
Message-ID: <20131127115634.GA10022@twins.programming.kicks-ass.net>
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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.